GEOL EXAM 2

A form of mass wasting composed of loose soil, rock, organic matter, air and water and caused by intense surface-water flow, due to heavy precipitation is known as________.

debris flow

A sill runs ________ to the surrounding rock.

parallel

A dike runs ________ to the surrounding rock.

perpendicular

Landslides and Falls

-Although many types of mass movements are included in the general term "landslide," the more restrictive use of the term refers only to mass movements, where there is a distinct zone of weakness that separates the slide material from more stable underlying material. The two major types of slides are rotational slides and translational slides. Rotational slide: This is a slide in which the surface of rupture is curved concavely upward and the slide movement is roughly rotational about an axis that is parallel to the ground surface and transverse across the slide (figure 2a). Translational slide: In this type of slide, the landslide mass moves along a roughly planar surface with little rotation or backward tilting (figure 2b). A block slide is a translational slide in which the moving mass consists of a single unit or a few closely related units that move downslope as a relatively coherent mass -When large amounts of rock suddenly break loose from a cliff or mountainside, they move quickly and with tremendous force (figure 3). Air trapped under the falling rocks acts as a cushion that keeps the rock from slowing down. Landslides and avalanches can move as fast as 200 to 300 km/hour -Landslides are exceptionally destructive. Homes may be destroyed as hillsides collapse. Landslides can even bury entire villages. Landslides may create lakes when the rocky material dams a stream. If a landslide flows into a lake or bay, they can trigger a tsunami -Landslides often occur on steep slopes in dry or semi-arid climates. The California coastline, with its steep cliffs and years of drought punctuated by seasons of abundant rainfall, is prone to landslides. At-risk communities have developed landslide warning systems. Around San Francisco Bay, the National Weather Service and the U.S. Geological Survey use rain gauges to monitor soil moisture. If soil becomes saturated, the weather service issues a warning. Earthquakes, which may occur on California's abundant faults, can also trigger landslides

Magmatic Dikes

-An intrusive dike is an igneous body with a very high aspect ratio, which means that its thickness is usually much smaller than the other two dimensions. Thickness can vary from sub-centimeter scale to many meters, and the lateral dimensions can extend over many kilometres. A dike is an intrusion into an opening cross-cutting fissure, shouldering aside other pre-existing layers or bodies of rock; this implies that a dike is always younger than the rocks that contain it. Dikes are usually high-angle to near-vertical in orientation, but subsequent tectonic deformation may rotate the sequence of strata through which the dike propagates so that the dike becomes horizontal. Near-horizontal, or conformable intrusions, along bedding planes between strata are called intrusive sills -Sometimes dikes appear in swarms, consisting of several to hundreds of dikes emplaced more or less contemporaneously during a single intrusive event. The world's largest dike swarm is the Mackenzie dike swarm in the Northwest Territories, Canada -Dikes often form as either radial or concentric swarms around plutonic intrusives, volcanic necks or feeder vents in volcanic cones. The latter are known as ring dikes -Dikes can vary in texture and their composition can range from diabase or basaltic to granitic or rhyolitic, but on a global perspective the basaltic composition prevails, manifesting ascent of vast volumes of mantle-derived magmas through fractured lithosphere throughout Earth history. Pegmatite dikes comprise extremely coarse crystalline granitic rocks—often associated with late-stage granite intrusions or metamorphic segregations. Aplite dikes are fine-grained or sugary-textured intrusives of granitic composition

Divergent plate boundaries

-At divergent plate boundaries hot mantle rock rises into the space where the plates are moving apart. As the hot mantle rock convects upward it rises higher in the mantle. The rock is under lower pressure; this lowers the melting temperature of the rock and so it melts. Lava erupts through long cracks in the ground, or fissures -Why does melting occur at divergent plate boundaries? Hot mantle rock rises where the plates are moving apart. This releases pressure on the mantle, which lowers its melting temperature. Lava erupts through long cracks in the ground, or fissures -Volcanoes erupt at mid-ocean ridges, such as the Mid-Atlantic ridge, where seafloor spreading creates new seafloor in the rift valleys. Where a hotspot is located along the ridge, such as at Iceland, volcanoes grow high enough to create islands

silicates

-Based on the polyatomic anion, (SiO4)4-, which has a tetrahedral shape. Most minerals in the earth's crust and mantle are silicate minerals. All silicate minerals are built of silicon-oxygen tetrahedra (SiO4)4- in different bonding arrangements which create different crystal lattices. You can understand the properties of a silicate mineral such as crystal shape and cleavage by knowing which type of crystal lattice it has -In nesosilicates, also called island silicates, the silicate tetrahedra are separate from each other and bonded completely to non silicate atoms. Olivine is an island silicate -In sorosilicates or paired silicates, such as epidote, the silicate tetrahedra are bonded in pairs -In cyclosilicates, also called ring silicates, the silicate tetrahedra are joined in rings. Beryl or emerald is a ring silicate -In phyllosilicates or sheet silicates, the tetrahedra are bonded at three corners to form flat sheets. Biotite is a sheet silicate -In single-chain inosilicates the silicate tetrahedra are bonded in single chains. Pyroxenes are singele-chain inosilicates -In double-chain inosilicates the silicate tetrahedra are bonded in double chains. Amphiboles are double-chain inosilicates -In tectosilicates, also known as framework silicates, all corners of the silicate tetrahedra are bonded to corners of other silicate tetrahedra, forming a complete framework of silicate tetrahedra in all directions. Feldspar, the most common mineral in earth's crust, and quartz are both framework silicates

Chemical Weathering by Acid Rain

-Carbon dioxide (CO2) combines with water as raindrops fall through the atmosphere. This makes a weak acid, called carbonic acid. Carbonic acid is a very common in nature where it works to dissolve rock -Pollutants, such as sulfur and nitrogen, from fossil fuel burning, create sulfuric and nitric acid. Sulfuric and nitric acids are the two main components of acid rain, which accelerate chemical weathering (figure 7). Acid rain is discussed in the Human Actions and the Atmosphere chapter

color

-Color is often useful, but should not be relied upon. Different minerals may be the same color -Additionally, Some minerals come in many different colors. Quartz, for example, may be clear, white, gray, brown, yellow, pink, red, or orange. So color can help, but do not rely on color as the determining property. Figure 3 shows one sample of quartz that is colorless and another quartz that is purple. A tiny amount of iron makes the quartz purple. Many minerals are colored by chemical impurities

Composition and Color

-Composition influences the color of igneous rocks. Felsic rocks tend to be light in color (white, pink, tan, light brown, light gray). Mafic rocks tend to be dark in color (black, very dark brown, very dark gray, dark green mixed with black). The color distinction comes from the differences in iron and magnesium content. Iron and, to a lessor extent, magnesium give minerals a darker color. Intermediate igneous rocks tend to have intermediate shades or colors (green, gray, brown) -The association between color and composition is useful because before you can name and interpret an igneous rock you need to determine both its texture AND its composition. If you have an aphanitic igneous rock, which has no crystals big enough to see without a microscope, you can estimate its composition based on its color: pink or nearly white, felsic; medium gray, intermediate; very dark or black, mafic -This color rule works most of the time but there are two problems that you need to keep in mind. First, the rule does not work for glassy igneous rocks. Obsidian, which is volcanic glass, is usually black, even though it has a felsic composition. That is because a tiny amount of iron, too little to color minerals very darkly, can color glass darkly -The second problem is that when igneous rocks have been exposed to air and water for a long time, they start to weather, which changes their color. Geologists working in the field carry a rock hammer, so they can break off the weathered, outer parts of rocks to see the "fresh," unweathered rock inside -If you can see and identify the minerals in an igneous rock, you can gain further information about the igneous composition. Igneous rocks with quartz in them are usually felsic. Igneous rocks with olivine in them are usually mafic. Igneous rocks with neither quartz nor olivine in them are most commonly intermediate

isotopes

-Every atom of a specific element must have the same number of protons in its nucleus. This number is its atomic number. However, there is a range of possible numbers of neutrons it can have in its nucleus. The fact that atoms of a chemical element may have different numbers of neutrons results in each chemical element having several isotopes. Isotopes are atoms of a given chemical element that have different numbers of neutrons in their nuclei -For example, while all atoms of the element oxygen have eight protons in their nuclei, those oxygen atoms may have eight, nine, or ten neutrons. The different numbers of neutrons in the nucleus distinguishes the three isotopes of oxygen. Oxygen-16 is the isotope of oxygen with 8 neutrons in its nucleus. The number 16 is called the atomic mass number. The atomic mass number is the total number of protons and neutrons in the nucleus of an isotope. From this definition, and knowing that all oxygen atoms have 8 protons in the nucleus, you can deduce that oxygen-17 is the oxygen isotope with 9 neutrons and oxygen-18 is the oxygen isotope with 10 neutrons. Abbreviated into symbols, the three isotopes of oxygen are written as 16O, 17O and 18O -Isotopes are not very important for understanding minerals, but are important in understanding how to apply chemistry and nuclear physics to geology, such as how to use measurements of radioactive isotopes to measure the ages of rocks and minerals and how to use oxygen isotopes from layers of glacial ice to determine what the temperature of the earth was during an ice age

Abrasion

-Gravity causes abrasion as rock material moves down-hill. Moving water causes abrasion as particles in the water collide. Abrasion makes rocks with sharp or jagged edges smooth and round, e.g. beach glass or cobbles in a stream -Plants and animals can also generate mechanical weathering- roots expanding into rock fissures or animals burrowing into soil and rock

chemical bonds

-If atoms interact with other atoms, they can gain or lose electrons to the other atoms, or share electrons with other atoms. In an individual atom, the most stable arrangement is a full outer shell of electrons. Therefore, chemical reactions will occur, and chemical bonds will form that hold atoms together to each other, when atoms encounter other atoms and change their electron configurations toward more stable, lower-energy arrangements, which generally involves achieving full outer electron shells in the atoms -This stable configuration—a full outer shell of electrons is exemplified by the inert gases. In the periodic table the inert gases are the elements of group 18 or VIIIA, the last column on the right. Inert gases do not have to undergo any chemical reactions or form any chemical bonds with other atoms in order to have a full outer shell of electrons. The inert gases already have full outer shells of electrons. That is why they are chemically inert. Their electrons are as stable as can be arranged. For this reason, inert gases are extremely unlikely to undergo any chemical reactions and it is almost impossible for them to bond with any other atoms. Because they do not bond with any other atoms to form a liquid, a solid, a molecule, or a mineral, the inert gases consist of atoms that stay separate from each other, in the gas state -Individual atoms of all the other chemical elements, when they are neutral atoms, do not have full outer shells of electrons like the inert gases do. Therefore, they do not have the most stable arrangement of electrons that they possibly can. That is why most chemical elements have a strong tendency to either gain or lose electrons, or to enter into other arrangements of their valence electrons, the electrons in their outer shell. Chemical reactions and chemical bonds are generally a result of electrons being rearranged within and among atoms to give the atoms full outer electron shells. For an atom to lose or gain one electron takes less energy than to lose or gain two, which in turn takes less energy than to lose or gain a third electron. For an individual atom to gain or lose four electrons will only occur in extremely high-energy environments such as in a star. In common chemical reactions on earth, and in the formation of chemical bonds, no element will completely gain or lose four electrons. This limits the charges of atomic cations to +1, +2 or +3 and the charges of atomic anions to -1, -2, or -3. -Reading this far, you have learned about one group of elements in the periodic table, group 18, the inert gases. Another group of chemical elements in the periodic table is the alkali elements. The alkali elements compose group 1 or IA, the left hand column, including the elements sodium (Na) and potassium (K). Hydrogen is not usually considered as an alkali element because, even though it is shown in group 1 in the periodic table. Hydrogen is so light and small, with just a single proton in its nucleus, that it has some unique behaviors and is considered in a class by itself. The alkali elements have a single electron in their outer electron shell. If an alkali element loses a single electron, it becomes an ion with a +1 charge and a full outer shell. If an opportunity arises, alkali elements will easily turned into +1 cations

Logging and Mining

-Logging removes trees that protect the ground from soil erosion. The tree roots hold the soil together and the tree canopy protects the soil from hard falling rain. Logging results in the loss of leaf litter, or dead leaves, bark, and branches on the forest floor. Leaf litter plays an important role in protecting forest soils from erosion -Much of the world's original forests have been logged. Many of the tropical forests that remain are currently the site of logging because North America and Europe have already harvested many of their trees (Figure 4). Soils eroded from logged forests clog rivers and lakes, fill estuaries, and bury coral reefs

Intrusive and Extrusive Igneous Rocks

-Igneous rocks are called intrusive when they cool and solidify beneath the surface. Intrusive rocks form plutons and so are also called plutonic. A pluton is an igneous intrusive rock body that has cooled in the crust. When magma cools within the Earth, the cooling proceeds slowly. Slow cooling allows time for large crystals to form, so intrusive igneous rocks have visible crystals. Granite is the most common intrusive igneous rock -Igneous rocks make up most of the rocks on Earth. Most igneous rocks are buried below the surface and covered with sedimentary rock, or are buried beneath the ocean water. In some places, geological processes have brought igneous rocks to the surface. Figure 2 below shows a landscape in California's Sierra Nevada made of granite that has been raised to create mountains -Igneous rocks are called extrusive when they cool and solidify above the surface. These rocks usually form from a volcano, so they are also called volcanic rocks -Extrusive igneous rocks cool much more rapidly than intrusive rocks. There is little time for crystals to form, so extrusive igneous rocks have tiny crystals

Identifying Igneous Rocks

-Igneous rocks can be distinguished from sedimentary rocks by the lack of beds, lack of fossils, and lack of rounded grains in igneous rocks, and the presence of igneous textures. A granite, for example, can be distinguished from a sandstone because rather than being a mixture of weathered, rounded grains compressed and cemented together, granite consists of a small number of minerals in shiny black, white, or pink colors, with excellent crystal forms, grown together into a completely interlocking pattern. Sandstones, by contrast, have sedimentary bedding (layers) and consist of rounded grains with some spaces between the grains, which you can see with a hand lens or magnifying glass -Igneous rocks can be distinguished from most regional metamorphic rocks by the lack of foliation (layering) in igneous rocks. Unfoliated metamorphic rocks lack igneous textures and usually contain minerals not found in igneous rocks. Granite may look like gneiss at first glance, but granite has no layering, no preferred orientation of the minerals. The minerals in a granite grow randomly in all directions, rather than tending to grow parallel to each other. Igneous rocks are classified on the basis of their texture and their composition. See the previous sections for descriptions of the different igneous textures and compositions. The igneous rock classification tables that accompany this section are arranged on the basis of igneous textures first, and further broken down on the basis of igneous composition. Remember that igneous composition is estimated on the basis of color: light = felsic composition, medium = intermediate composition, and dark = mafic composition

characteristics of igneous rocks

-Igneous rocks contain three essential sources of information: their minerals, their overall chemical composition, and their igneous texture. Igneous rock names are based on specific combinations of these features. Igneous rocks also contain isotopic information that is used in determining absolute ages and in further characterizing the origin of the magma. Special equipment and expertise is required to conduct isotopic and precise chemical analyses. Fortunately, with some basic training and practice anyone can learn to identify the minerals, composition and texture of an igneous rock; name the rock; and interpret key information about its origins -All igneous rocks, other than pure volcanic glass, contain minerals. The minerals provide details on the chemical composition of the rock, and on the conditions in which the magma originated, cooled, and solidified. Geologists conduct chemical analyses of minerals to determine the temperatures and pressures at which they formed and to identify the dissolved gases and chemical elements that were present in the magma -Most magmas are predominantly silicate liquids, composed largely of silica tetrahedra that have not yet bonded together to become silicate minerals. The chemical composition of an igneous rock tells us about the origin of the magma, beginning with which type of rock melted within the earth to form the magma in the first place, and how deep in the earth the melting occurred. Once magma has formed inside the earth, its composition may be modified. Minerals can grow from the magma and separate from it, changing the chemistry of the remaining liquid. Or, one body of magma can mix with another that has a different composition -Magmas come in a range of compositions, from rich in silica and poor and iron and magnesium (felsic) to moderate in silica and high in iron and magnesium (mafic). Felsic igneous rocks, as a whole rock, tend to have light colors or shades: white, pink, light brown, light gray. Mafic igneous rocks, on the whole, tend to be dark colored, commonly black or dark gray. Most mafic magma originates by melting of rocks in the mantle that are extremely rich in iron and magnesium. Felsic magma usually originates in the crust or by the shedding of mafic minerals as magma rises through the crust -The igneous texture tells us how the magma cooled and solidified. Magma can solidify into igneous rock in several different ways, each way resulting in a different igneous texture. Magma may stay within the earth, far below ground level, and crystallize into plutonic igneous rock (also known as intrusive igneous rock). Or, magma may flow out onto surface of the earth as a lava flow. Another way that igneous rock forms is by magma erupting explosively into the air and falling to earth in pieces known as pyroclastic material, also called tephra. Lava flows and pyroclastic material are volcanic igneous rock (also known as extrusive igneous rock) -The igneous texture of a rock is not how it feels in your hand, not whether it is rough or smooth. The igneous texture describes whether the rock has mineral crystals or is glassy, the size of the mineral grains, and the rock's porosity (empty spaces)

Uses of Igneous Rocks

-Igneous rocks have a wide variety of uses. One important use is as stone for buildings and statues. Diorite was used extensively by ancient civilizations for vases and other decorative artwork and is still used for art today -Granite (Figure 7) is used both in building construction and for statues. It is also a popular choice for kitchen countertops. Peridotite is sometimes mined for peridot, a type of olivine that is used in jewelry -Pumice is commonly used as an abrasive. Pumice is used to smooth skin or scrape up grime around the house. When pumice is placed into giant washing machines with newly manufactured jeans and tumbled, the result is "stone-washed" jeans. Ground up pumice stone is sometimes added to toothpaste to act as an abrasive material to scrub teeth

Slump and Creep

-Less dramatic types of downslope movement move earth materials slowly down a hillside. Slump moves materials as a large block along a curved surface (figure 7). Slumps often happen when a slope is undercut, with no support for the overlying materials, or when too much weight is added to an unstable slope -Creep is the imperceptibly slow, steady, downward movement of slope-forming soil or rock. Movement is caused by shear stress sufficient to produce permanent deformation, but too small to produce shear failure. There are generally three types of creep: 1. Seasonal, where movement is within the depth of soil affected by seasonal changes in soil moisture and soil temperature 2. Continuous, where shear stress continuously exceeds the strength of the material 3. Progressive, where slopes are reaching the point of failure as other types of mass movements. Creep is indicated by curved tree trunks, bent fences or retaining walls, tilted poles or fences, and small soil ripples or ridges Curves in tree trunks indicate creep because the base of the tree is moving downslope while the top is trying to grow straight up (figure 8). Tilted telephone or power company poles are also signs of creep.

volcanic rocks

-Magmas that erupt as lava onto the earth's surface cool and solidify rapidly. Rapid cooling results in an aphanitic igneous texture, in which few or none of the individual minerals are big enough to see with the naked eye. This is sometimes referred to as a fine-grained igneous texture -Some lava flows, however, are not purely fine-grained. If some mineral crystals start growing while the magma is still underground and cooling slowly, those crystals grow to a large enough size to be easily seen, and the magma then erupts as a lava flow, the resulting texture will consist of coarse-grained crystals embedded in a fine-grained matrix. This texture is called porphyritic -If lava has bubbles of gas escaping from it as it solidifies, it will end up with "frozen bubble holes" in it. These "frozen bubble holes" are called vesicles, and the texture of a rock containing them is said to be vesicular. If so many bubbles are escaping from lava that it ends up containing more bubble holes than solid rock, the resulting texture is said to be frothy. Pumice is the name of a type of volcanic rock with a frothy texture. If lava cools extremely quickly, and has very little water dissolved in it, it may freeze into glass, with no minerals (glass by definition is not a mineral, because it does not have a crystal lattice). Such a rock is said to have a glassy texture. Obsidian is the common rock that has a glassy texture, and is essentially volcanic glass. Obsidian is usually black -Now let us briefly consider textures of tephra or pyroclastic rocks. Like lava flow rocks, these are also extrusive igneous rocks. However, instead of originating from lava that flowed on the earth's surface, tephra is volcanic material that was hurled through the air during a volcanic eruption. A pyroclastic rock made of fine-grained volcanic ash may be said to have a fine-grained, fragmental texture. Volcanic ash consists mainly of fine shards of volcanic glass. It may be white, gray, pink, brown, beige, or black in color, and it may have some other fine crystals and rock debris mixed in. The term "fine-grained, fragmental" is easy to confuse with the term fine-grained (aphanitic). An equivalent term that is less ambiguous is tuffaceous. Rocks made of volcanic ash are called tuff. A pyroclastic rock with many big chunks of material in it that were caught up in the explosive eruption is said to have a coarse-grained, fragmental texture. However, a better word that will avoid confusion is to say it has a brecciated texture, and the rock is usually called a volcanic breccia. The bigger chunks of material in a volcanic breccia are more than 1 cm (5/8 inch) across, and sometimes are much bigger

Melting

-Melting at convergent plate boundaries has many causes. The subducting plate heats up as it sinks into the mantle. Also, water is mixed in with the sediments lying on top of the subducting plate. As the sediments subduct, the water rises into the overlying mantle material and lowers its melting point. Melting in the mantle above the subducting plate leads to volcanoes within an island or continental arc -Why does melting occur at convergent plate boundaries? The subducting plate heats up as it sinks into the mantle. Also, water is mixed in with the sediments lying on top of the subducting plate. This water lowers the melting point of the mantle material, which increases melting. Volcanoes at convergent plate boundaries are found all along the Pacific Ocean basin, primarily at the edges of the Pacific, Cocos, and Nazca plates. Trenches mark subduction zones, although only the Aleutian Trench and the Java Trench appear on the map in figure 3 -Remember your plate tectonics knowledge. Large earthquakes are extremely common along convergent plate boundaries. Since the Pacific Ocean is rimmed by convergent and transform boundaries, about 80% of all earthquakes strike around the Pacific Ocean basin (the ring of fire). Why are 75% of the world's volcanoes found around the Pacific basin? Of course, these volcanoes are caused by the abundance of convergent plate boundaries around the Pacific

chemical reactions

-Minerals form as a result of chemical reactions. Chemical reactions are driven mainly by the arrangement and rearrangement of electrons in atoms. In a mineral, the atoms are held together by chemical bonds, which derive from the electrons -Electrons can be thought of as occupying energy levels, or shells, in an atom. The lowest-energy shell is closest to the nucleus. Each shell can accommodate only a limited number of electrons. The first shell can hold two electrons, the second and third shells can hold eight electrons, and the next two shells can hold eighteen electrons. Unless energy is added to an atom to excite it from its low-energy state, the electrons in the atom will occupy the lowest-energy shells available to them -The Bohr model (see Figure 3) was developed by Niels Bohrs in 1913. In this model, electrons exist within principal shells. An electron normally exists in the lowest energy shell available, which is the one closest to the nucleus. Energy from a photon of light can bump it up to a higher energy shell, but this situation is unstable, and the electron quickly decays back to the ground state

periodic table

-Naturally occurring atoms found in the earth range from hydrogen, with just one proton in its nucleus, to uranium, with 92 protons in its nucleus. These are the naturally occurring chemical elements, which includes such commonly known elements as carbon, oxygen, iron, and so on. The periodic table lists all the chemical elements in a way that tells us how many protons each of them has, how its electrons are arranged, and what the general chemical behavior of each element is -eighteen groups and seven periods Two additional rows of elements, known as the lanthanides and actinides, are placed beneath the main table. These elements are placed separately to make the table more compact. All the elements in a group have a similar chemical behavior. This is because all the elements in a group have a similar arrangement of electrons in their atoms, and it is the electron arrangement that determines the chemical behavior of an element -For each element, the name, atomic symbol, atomic number, and atomic mass are provided. The atomic number is a whole number that represents the number of protons: each chemical element is distinguished by the number of protons in its nucleus. For example, every atom of the element oxygen has eight protons in its nucleus. That is why the atomic number of oxygen is 8. If an atom has greater or fewer than eight protons in its nucleus, it is not oxygen, it is some other chemical element. In the periodic table, the atomic number of each element is listed above the chemical symbol of the element -The atomic mass, which is the average mass of different isotopes, is estimated to two decimal places. For example, hydrogen has the atomic symbol H, the atomic number 1, and an atomic mass of 1.01. The atomic mass is always larger that the atomic number. For most small elements, the atomic mass is approximately double the atomic number, as the number of protons and neutrons is about equal -The elements are divided into three categories: metals, nonmetals and metalloids. These form a diagonal line from period two, group thirteen to period seven, group sixteen. All elements to the left of the metalloids are metals, and all elements to the right are nonmetals. The periodic table was created to help chemists better understand elements and how they function. It is a map to elemental behavior.

ionic bonds

-Now look at group 17 or VIIA in the periodic table, which includes the chemical elements fluorine (F), chlorine (Cl) and so on. These are the halogen elements. If a halogen element gains a single electron, it becomes an ion with a-1 charge and a full outer electron shell. If an opportunity arises, halogen elements have a strong tendency to take in an extra electron and become -1 anions because by doing so they achieve a full outer shell of electrons, which is the most stable arrangement of electrons possible -If sodium and chlorine atoms get together in the right conditions, such as in an evaporating solution of salt water, each sodium atoms will give up an electron to a chlorine atom. This turns the sodium atoms into sodium ions, Na+, and the chlorine atoms into chloride ions, Cl-. Opposite electrical charges attract, so the sodium ions and chloride ions will tend to stick together with each other, joined by what are called ionic bonds -Not only will the sodium and chloride ions have a very strong tendency to join together with each other via ionic bonds, in most situations they will naturally arrange into a configuration where there is no wasted space and no wasted energy. This leads them to form the crystal lattice of the mineral halite. Halite is a mineral with the chemical formula NaCl, sodium chloride, in which the bonds between the atoms are all ionic bonds -Look at the diagram of halite showing the sodium and chloride ions arranged into the crystal lattice. All the ionic bonds are at the same angle and the same distance, so they are all of equal strength. This is the lowest-energy arrangement of the ions, the most stable arrangement. If any of the ions were spaced located at different angles or at different distances, there would be extra energy available. This extra energy would drive the ions toward equal angles and distances from each other, until the extra energy is used up and the ions are arranged into their lowest energy state. That is why minerals form, as a natural way for atoms to arrange themselves into the lowest energy state currently available to them

Pyroclastic Deposits

-Pyroclastic rocks or pyroclastics are clastic rocks composed solely or primarily of volcanic materials. Where the volcanic material has been transported and reworked through mechanical action, such as by wind or water, these rocks are termed volcaniclastic. Commonly associated with unsieved volcanic activity—such as Plinian or krakatoan eruption styles, or phreatomagmatic eruptions—pyroclastic deposits are commonly formed from airborne ash, lapilli and bombs or blocks ejected from the volcano itself, mixed in with shatteredcountry rock -Pyroclastic rocks may be a range of clast sizes, from the largest agglomerates, to very fine ashes and tuffs. Pyroclasts of different sizes are classified as volcanic bombs, lapilli, and volcanic ash. Ash is considered to be pyroclastic because it is a fine dust made up of volcanic rock. One of the most spectacular forms of pyroclastic deposit are the ignimbrites, deposits formed by the high-temperature gas-and-ash mix of a pyroclastic flow event

Slides and Falls

-Rocks that fall to the base of a cliff make a talus slope (figure 1).We call the initial drop a "fall" where a rock travels through the air.If the talus slope becomes "over-steepened" then the mass will slide downhill.What makes for a downslope movements?=> These are governed by gravity, mechanical weathering, and the presence of interstitial water -Landslides and avalanches are the most dramatic, sudden, and dangerous examples of earth materials moved by gravity. Landslides are sudden falls of rock, whereas avalanches are sudden falls of snow

covalent bonds

-Some elements, such as carbon (C) and silicon (Si) have a half-full valence shell. (The valence shell is another name for the outer shell, where the most reactive electrons are.) If an element such as carbon were to gain 4 electrons or lose 4 electrons, it would have a full valence shell. However, it is very difficult for an atom to gain or lose four electrons—the energy barrier becomes too strong. Therefore, carbon and silicon, along with a few other elements, tend to form a different type of bond in which they share their outer electrons with other atoms, which in turn share their outer electrons with the carbon (or silicon) atom. The atoms all end up with a full outer shell of electrons, even though some or all of those electrons are being shared with neighboring atoms. This electron sharing keeps the atoms bonded together. This type of chemical bond is called a covalent bond -It is not uncommon for covalent bonds to be relatively strong. An extreme example can be in diamond. Diamond is a mineral consisting of nothing but carbon atoms, so its chemical formula is simply C. Each carbon atom in the diamond crystal lattice is covalently bonded to—sharing its valence electrons with—four neighboring carbon atoms. A diamond crystal is held together by nothing but extremely strong covalent bonds in all directions, which makes diamond a very hard mineral, the hardest known

Pacific Rim

-The Pacific Ring of Fire is where the majority of the volcanic activity on the Earth occurs. A description of the Pacific Ring of Fire along western North America is a description of the plate boundaries -Subduction at the Middle American Trench creates volcanoes in Central America. The San Andreas Fault is a transform boundary. Subduction of the Juan de Fuca plate beneath the North American plate creates the Cascade volcanoes. Subduction of the Pacific plate beneath the North American plate in the north creates the Aleutian Islands volcanoes -Volcanoes at convergent plate boundaries are found all along the Pacific Ocean basin, primarily at the edges of the Pacific, Cocos, and Nazca plates. Trenches mark subduction zones -The Cascades are a chain of volcanoes at a convergent boundary where an oceanic plate is subducting beneath a continental plate. Specifically the volcanoes are the result of subduction of the Juan de Fuca, Gorda, and Explorer Plates beneath North America. The volcanoes are located just above where the subducting plate is at the right depth in the mantle for there to be melting -The Cascades have been active for 27 million years, although the current peaks are no more than 2 million years old. The volcanoes are far enough north and are in a region where storms are common, so many are covered by glaciers

Hotspot volcanic chains

-The joint mantle plume/hotspot hypothesis envisages the feeder structures to be fixed relative to one another, with the continents and seafloor drifting overhead. The hypothesis thus predicts that time-progressive chains of volcanoes are developed on the surface. Examples are Yellowstone, which lies at the end of a chain of extinct calderas, which become progressively older to the west. Another example is the Hawaiian archipelago, where islands become progressively older and more deeply eroded to the northwest -Geologists have tried to use hotspot volcanic chains to track the movement of the Earth's tectonic plates. This effort has been vexed by the lack of very long chains, by the fact that many are not time-progressive (e.g. the Galápagos) and by the fact that hotspots do not appear to be fixed relative to one another (e.g. Hawaii and Iceland)

other identifying characteristics

-There are some properties that only help to distinguish a small number of minerals, or even just a single mineral. An example of such a special property is the effervescent reaction of calcite to a weak solution of hydrochloric acid (5% HCl). Calcite fizzes or effervesces as the HCl solution dissolves it and creates CO2 gas. Calcite is easy to identify even without testing the reaction to HCl, by its hardness, luster and cleavage -Another special property is magnetism. This can be tested by seeing if a small magnet responds to the mineral. The most common mineral that is strongly magnetic is the mineral magnetite. A special property that shows up in some sample of plagioclase feldspar is its tendency to exhibit striations on cleavage surfaces. Striations are perfectly straight, fine, parallel lines. Magnification may be required to see striations on plagioclase cleavage surfaces. Other special properties may be encountered on a mineral to mineral basis

Weathering Versus Erosion

-Weathering and erosion sort of sound like the same thing, but geologists make a fairly simple distinction.With weathering, we are merely speaking of the in situ breakdown of rock material without transport. In other words, weathering involves rocks breaking apart along fractures but not moving from the site of disaggregation. As you'll find below, we then categorize weathering as either mechanical or chemical (depending on whether or not the rock material changes chemical composition) -In the case of erosion, rock material is actually being moved from the site of weathering. It can be moved by gravity (fall, roll), or by moving water (probably the most common) or by air (wind)

plutonic rocks

-When magma cools slowly underground and solidifies there, it usually grows crystals big enough to be seen easily with the naked eye. These visible crystals comprise the whole rock, not just part of it as in a porphyritic, fine-grained igneous rock. The texture of an igneous rock made up entirely of crystals big enough to be easily seen with the naked eye is phaneritic. Phaneritic texture is sometimes referred to as coarse-grained igneous texture. Granite, the most well known example of an intrusive igneous rock, has a phaneritic texture -Sometimes an intrusion of magma that is crystallizing slowly underground releases large amounts of hot water. The water is released from the magma as extremely hot fluid with lots of chemical elements dissolved in it. This hydrothermal fluid gets into cracks and voids in the earth's crust, and as it cools it may grow very large minerals from the dissolved chemical elements. A rock consisting of such large minerals is said to have a pegmatitic texture, which means the average mineral size is greater than 1 cm in diameter (and sometimes is much larger). The name of an igneous rock with a pegmatitic texture is pegmatite. Pegmatites are commonly found in or near the margins of bodies of granite

fracture

-a break in a mineral that is not along a cleavage plane. Fracture is not always the same in the same mineral because fracture is not determined by the structure of the mineral -Minerals may have characteristic fractures (Figure 9). Metals usually fracture into jagged edges. If a mineral splinters like wood, it may be fibrous. Some minerals, such as quartz, form smooth curved surfaces when they fracture -All minerals have fracture. Fracture is breakage, which occurs in directions that are not cleavage directions. Some minerals, such as quartz, have no cleavage whatsoever. When a mineral with no cleavage is broken apart by a hammer, it fractures in all directions. Quartz is said to exhibit conchoidal fracture. Conchoidal fracture is the way a thick piece of glass breaks with concentric, curving ridges on the broken surfaces. However, some quartz crystals have so many flaws that instead of exhibiting conchoidal fracture they simply exhibit irregular fracture. Irregular fracture is a standard term for fractures that do not exhibit any of the qualities of the other fracture types. In introductory geology, the key fracture types to remember are irregular, which most minerals exhibit, and conchoidal, seen in quartz

dikes

-a sheet of rock that formed in a fracture in a pre-existing rock body. Dikes can be either magmatic or sedimentary in origin. Magmatic dikes form when magma intrudes into a crack then crystallizes as a sheet intrusion, either cutting across layers of rock or through an unlayered mass of rock. Clastic dikes are formed when sediment fills a pre-existing crack

sills

-a tabular sheet intrusion that has intruded between older layers of sedimentary rock, beds of volcanic lava or tuff, or even along the direction of foliation in metamorphic rock. The term sill is synonymous with concordant intrusive sheet. This means that the sill does not cut across preexisting rocks, in contrast to dikes, discordant intrusive sheets which do cut across older rocks. Sills are fed by dikes, except in unusual locations where they form in nearly vertical beds attached directly to a magma source. The rocks must be brittle and fracture to create the planes along which the magma intrudes the parent rock bodies, whether this occurs along preexisting planes between sedimentary or volcanic beds or weakened planes related to foliation in metamorphic rock. These planes or weakened areas allow the intrusion of a thin sheet-like body of magma paralleling the existing bedding planes, concordant fracture zone, or foliations -Sills parallel beds (layers) and foliations in the surrounding country rock. They can be originally emplaced in a horizontal orientation, although tectonic processes may cause subsequent rotation of horizontal sills into near vertical orientations. Sills can be confused with solidified lava flows; however, there are several differences between them. Intruded sills will show partial melting and incorporation of the surrounding country rock. On both contact surfaces of the country rock into which the sill has intruded, evidence of heating will be observed (contact metamorphism). Lava flows will show this evidence only on the lower side of the flow. In addition, lava flows will typically show evidence of vesicles (bubbles) where gases escaped into the atmosphere. Because sills generally form at shallow depths (up to many kilometers) below the surface, the pressure of overlying rock prevents this from happening much, if at all. Lava flows will also typically show evidence of weathering on their upper surface, whereas sills, if still covered by country rock, typically do not

atoms

-consist of protons, neutrons, and electrons. Protons have a positive (+) electrical charge. Electrons have a negative (−) charge that is exactly equal and opposite to the electrical charge of a proton. Neutrons are electrically neutral. -Most of the mass of an atom is packed into its tiny nucleus. An atomic nucleus is made of protons and neutrons, which have approximately the same mass (about 1.67 × 10−24 grams). Electrons, on the other hand, are arranged in specific orbitals around the nucleus of an atom; they are also much smaller in mass than protons and neutrons, weighing only 9.11 × 10−28 grams, or about 1/1800 the weight of protons and neutrons -Even though the mass of an electron is a tiny mass compared to the mass of a proton or a neutron, the electrons occupy most of the volume of an atom

density

-describes how much matter is in a certain amount of space: density = mass/volume -Mass is a measure of the amount of matter in an object. The amount of space an object takes up is described by its volume. The density of an object depends on its mass and its volume. For example, the water in a drinking glass has the same density as the water in the same volume of a swimming pool -specific gravity of a substance compares its density to that of water. Substances that are more dense have higher specific gravity

luster

-describes the reflection of light off a mineral's surface. Mineralogists have special terms to describe luster. One simple way to classify luster is based on whether the mineral is metallic or non-metallic. Minerals that are opaque and shiny, such as pyrite, have a metallic luster. Minerals such as quartz have a non-metallic luster -Luster is how the surface of a mineral reflects light. It is not the same thing as color, so it crucial to distinguish luster from color. For example, a mineral described as "shiny yellow" is being described in terms of luster ("shiny") and color ("yellow"), which are two different physical properties. Standard names for luster include metallic, glassy, pearly, silky, greasy, and dull. It is often useful to first determine if a mineral has a metallic luster. A metallic luster means shiny like polished metal. For example cleaned polished pieces of chrome, steel, titanium, copper, and brass all exhibit metallic luster as do many other minerals. Of the nonmetallic lusters, glassy is the most common and means the surface of the mineral reflects light like glass. Pearly luster is important in identifying the feldspars, which are the most common type of mineral. Pearly luster refers to a subtle irridescence or color play in the reflected light, same way pearls reflect light. Silky means relecting light with a silk-like sheen. Greasy luster looks similar to the luster of solidified bacon grease. Minerals with dull luster reflect very little light. Identifying luster takes a little practice. Remember to distinguish luster from color

Chemical weathering

-different from mechanical weathering because the rock actually changes chemical composition via reaction with things like water, acid rain, and air itself.Mineral changes take place -Some minerals are particularly unstable under surface conditions- those are typically minerals that initially form at high pressure or high temperatures deep in the earth. Examples include olivine and pyroxene -When these rocks reach the Earth's surface, they are now at very low temperatures and pressures. This is a very different environment from the one in which they formed and the minerals are no longer stable -Chemical weathering changes minerals that were stable inside the earth to ones that are stable at Earth's surface. For example, clay minerals are stable at the surface and chemical weathering converts many minerals to clay

Igneous textures

-include the rock textures occurring in igneous rocks. Igneous textures are used by geologists in determining the mode of origin igneous rocks and are used in rock classification. There are six main types of textures; phaneritic, aphanitic, porphyritic, glassy, pyroclastic and pegmatitic -Aphanitic (a = not, phaner = visible) rocks in contrast to phaneritic rocks, typically form from lava which crystallize rapidly on or near Earth' surface. Because extrusive rocks make contact with the atmosphere they cool quickly, so the minerals do not have time to form large crystals. The individual crystals in an aphanitic igneous rock are not distinguishable to the naked eye. Examples of aphanitic igneous rock include basalt, andesite andrhyolite -Glassy or vitreous textures occur during some volcanic eruptions when the lava is quenched so rapidly that crystallization cannot occur. The result is a natural amorphous glass with few or no crystals. Examples includeobsidian and pumice -Pegmatitic texture occurs during magma cooling when some minerals may grow so large that they become massive (the size ranges from a few centimetres to several metres). This is typical of pegmatites -Phaneritic (phaner = visible) textures are typical of intrusive igneous rocks, these rocks crystallized slowly below Earth's surface. As magma cools slowly the minerals have time to grow and form large crystals. The minerals in a phaneritic igneous rock are sufficiently large to see each individual crystal with the naked eye. Examples of phaneritic igneous rocks are gabbro, diorite and granite -Porphyritic textures develop when conditions during cooling of a magma change relatively quickly. The earlier formed minerals will have formed slowly and remain as large crystals, whereas, sudden cooling causes the rapid crystallization of the remainder of the melt into a fine grained (aphanitic) matrix. The result is an aphanitic rock with some larger crystals (phenocrysts) imbedded within its matrix. Porphyritic texture also occurs when magma crystallizes below a volcano but is erupted before completing crystallization thus forcing the remaining lava to crystallize more rapidly with much smaller crystals -Pyroclastic (pyro = igneous, clastic = fragment) textures occur when explosive eruptions blast the lava into the air resulting in fragmental, typically glassy material which fall as volcanic ash, lapilli and volcanic bombs

ions

-neutral atom has the same number of electrons as it does protons. An atom that has lost or gained any electrons is no longer an electrically neutral atom. That type of atom, which is not electrically neutral and has an electrical charge associated with it, is called an ion. Atoms that have gained electrons are negatively (−) charged ions, or anions. Atoms that have lost electrons are positively (+) charged ions, or cations -It is also possible to have ions that are actually small groups of atoms bonded together. These are known as polyatomic ions. One example of a polyatomic ion is the carbonate ion, (CO3)2−, which has two extra electrons, giving it the net electrical charge of 2−

streak

-the color of a mineral's powder. Streak is a more reliable property than color because streak does not vary. Minerals that are the same color may have a different colored streak. Many minerals, such as the quartz in the Figure 3, do not have streak -to check streak, scrape the mineral across an unglazed porcelain plate (Figure 5). Yellow-gold pyrite has a blackish streak, another indicator that pyrite is not gold, which has a golden yellow streak

cleavage

-the tendency of a mineral to break along certain planes to make smooth surfaces. Halite breaks between layers of sodium and chlorine to form cubes with smooth surfaces -A mineral that naturally breaks into perfectly flat surfaces is exhibiting cleavage. Not all minerals have cleavage. A cleavage represents a direction of weakness in the crystal lattice. Cleavage surfaces can be distinguished by how they consistently reflect light, as if polished, smooth, and even. The cleavage properties of a mineral are described in terms of the number of cleavages and, if more than one cleavage, the angles between the cleavages. The number of cleavages is the number or directions in which the mineral cleaves. A mineral may exhibit 100 cleavage surfaces parallel to each other. Those represent a single cleavage because the surfaces are all oriented in the same diretion. The possible number of cleavages a mineral may have are 1,2,3,4, or 6. If more than 1 cleavage is present, and a device for measuring angles is not available, simply state whether the cleavages intersect at 90° or not 90° -to see mineral cleavage, hold the mineral up beneath a strong light and move it around, move it around some more, to see how the different sides reflect light. A cleavage direction will show up as a smooth, shiny, evenly bright sheen of light reflected by one set of parallel surfaces on the mineral -Minerals can cleave into polygons. Fluorite forms octahedrons -One reason gemstones are beautiful is that the cleavage planes make an attractive crystal shape with smooth faces

Chemical Weathering by Water

A water molecule has a very simple chemical formula, H2O, two hydrogen atoms bonded to one oxygen atom. But water is pretty remarkable in terms of all the things it can do. Remember from the Earth's Minerals chapter that water is a polar molecule. The positive side of the molecule attracts negative ions and the negative side attracts positive ions. So water molecules separate the ions from their compounds and surround them. Water can completely dissolve some minerals, such as salt

Lahars and Mudflow

Added water creates natural hazards produced by gravity (figure 5). On hillsides with soils rich in clay, little rain, and not much vegetation to hold the soil in place, a time of high precipitation will create a mudflow. Mudflows follow river channels, washing out bridges, trees, and homes that are in their path

Farming and Grazing

Agriculture is probably the most significant activity that accelerates soil erosion because of the amount of land that is farmed and how much farming practices disturb the ground (Figure 1). Farmers remove native vegetation and then plow the land to plant new seeds

crystal shape

All minerals are crystalline, but only some have the opportunity to exhibit the shapes of their crystals, their crystal forms. Many minerals in an introductory geology lab do not exhibit their crystal form. If a mineral has space while it grows, it may form natural crystals, with a crystal shape reflecting the geometry of the mineral's internal crystal lattice. The shape of a crystal follows the symmetry of its crystal lattice. Quartz, for instance, forms six-sided crystals, showing the hexagonal symmetry of its crystal lattice. There are two complicating factors to remember here: (1) minerals do not always form nice crystals when they grow, and (2) a crystal face is different from a cleavage surface. A crystal face forms during the growth of the mineral. A cleavage surface is formed when the mineral is broken

hydrogen bonds

Another type of chemical bond that occurs in some minerals is the hydrogen bond. Hydrogen bonds are caused by the positive and negative ends of polar molecules attracting each other strongly enough to hold each other in fixed positions. For example, water molecules can join together through hydrogen bonds to form the mineral known as ice. In a water molecule, H2O, each of the hydrogen atoms forms a covalent bond with the oxygen atom

Topsoil

Called the A horizon, the topsoil is usually the darkest layer of the soil because it has the highest proportion of organic material. The topsoil is the region of most intense biological activity: insects, worms, and other animals burrow through it and plants stretch their roots down into it. Plant roots help to hold this layer of soil in place. In the topsoil, minerals may dissolve in the fresh water that moves through it to be carried to lower layers of the soil. Very small particles, such as clay, may also get carried to lower layers as water seeps down into the ground

Associated Ore Deposits

Certain layered intrusions are a variety of sill that often contain important ore deposits. Precambrian examples include the Bushveld, Insizwa and the Great Dyke complexes of southern Africa, the Duluth intrusive complex of the Superior District, and the Stillwater igneous complex of the United States. Phanerozoic examples are usually smaller and include the Rùm peridotite complex of Scotland and the Skaergaard igneous complex of east Greenland. These intrusions often contain concentrations of gold, platinum, chromium and other rare elements

Convergent Plate Boundaries

Converging plates can be oceanic, continental, or one of each. If both are continental they will smash together and form a mountain range. If at least one is oceanic, it will subduct. A subducting plate creates volcanoes. Locations with converging in which at least one plate is oceanic at the boundary have volcanoes

Transgressive Sills

Despite their concordant nature, many large sills change stratigraphic level within the intruded sequence, with each concordant part of the intrusion linked by relatively short dike-like segments. Such sills are known as transgressive, examples include the Whin Sill and sills within the Karoo basin.[4] The geometry of large sill complexes in sedimentary basins has become clearer with the availability of 3D seismic reflection data.[5] Such data has shown that many sills have an overall saucer shape and that many others are at least in part transgressive

Color, Streak, and Luster

Diamonds are popular gemstones because the way they reflect light makes them very sparkly. Turquoise is prized for its striking greenish-blue color. Notice that specific terms are being used to describe the appearance of minerals

Continental Rifting

Eruptions are found at divergent plate boundaries as continents break apart. The volcanoes in Figure 6 are in the East African Rift between the African and Arabian plates. Remember from the chapter Plate Tectonics that Baja California is being broken apart from mainland Mexico as another example of continental rifting

metallic bonds

Gold forms a naturally occurring mineral of more or less pure gold, Au, held together by another type of bond, the metallic bond. Metallic elements such as gold and copper, when they bond with other metallic elements, are sharing some of their electrons not just with adjacent atoms, but throughout the whole substance. That is why metallic substances such as copper, gold, and aluminum make such good electrical conductors, because it is so easy to get the "loose" electrons to respond through the whole extent of the metal.

Volcanoes Hotspots

In geology, the places known as hotspots or hot spots are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the surrounding mantle. They may be on, near to, or far from tectonic plate boundaries. Currently, there are two hypotheses that attempt to explain their origins. One suggests that they are due to hot mantle plumes that rise as thermal diapirs from the core-mantle boundary. An alternative hypothesis postulates that it is not high temperature that causes the volcanism, but lithospheric extension that permits the passive rising of melt from shallow depths. This hypothesis considers the term "hotspot" to be a misnomer, asserting that the mantle source beneath them is, in fact, not anomalously hot at all. Well known examples include Hawaii and Yellowstone

Origins of Igneous Rocks

Once you have determined the texture and composition of an igneous rock, you can name it and you can also say something important about how it formed. For example, a coarse-grained, felsic igneous rock is not only a granite, it is an intrusive igneous rock that formed from slow cooling and crystallization of a body of magma within the earth's crust. The intrusion of large bodies of granite—batholiths—is usually part of the origin of a mountain range. Similarly, a fine-grained, mafic igneous rock is not only a basalt, it is an extrusive igneous rock that formed from rapid cooling and crystallization of a lava flow at earth's surface

Chemical Weathering by Oxygen

Oxidation is a chemical reaction that takes place when oxygen reacts with another element. Oxygen is very strongly chemically reactive. The most familiar type of oxidation is when iron reacts with oxygen to create rust (figure 8). Minerals that are rich in iron break down as the iron oxidizes and forms new compounds. Iron oxide produces the red color in soils

Subsoil

The B horizon or subsoil is where soluble minerals and clays accumulate. This layer is lighter brown and holds more water than the topsoil because of the presence of iron and clay minerals. There is less organic material

Sedimentary Dikes

Sedimentary dikes or clastic dikes are vertical bodies of sedimentary rock that cut off other rock layers. They can form in two ways: When a shallow unconsolidated sediment is composed of alternating coarse grained andimpermeable clay layers the fluid pressure inside the coarser layers may reach a critical value due to lithostatic overburden. Driven by the fluid pressure the sediment breaks through overlying layers and forms a dike. When a soil is under permafrost conditions the pore water is totally frozen. When cracks are formed in such rocks, they may fill up with sediments that fall in from above. The result is a vertical body of sediment that cuts through horizontal layers: a dike.

C horizon

The C horizon is a layer of partially altered bedrock. There is some evidence of weathering in this layer, but pieces of the original rock are seen and can be identified. Not all climate regions develop soils, and not all regions develop the same horizons. Some areas develop as many as five or six distinct layers, while others develop only very thin soils or perhaps no soils at all

Igneous Rock Compositions

The most common igneous compositions can be summarized in three words: mafic (basaltic), intermediate (andesitic), and felsic (granitic). Felsic composition is higher in silica (SiO2) and low in iron (Fe) and magnesium (Mg). Mafic composition is higher in iron and magnesium and lower in silica. Intermediate compositions contain silica, iron, and magnesium in amounts that are intermediate to felsic and mafic compositions

carbonates

These are based on the carbonate ion, (CO3)2-. Calcite, CaCO3, and dolomite, CaMg(CO3)2, are carbonate minerals. Carbonate minerals tend to dissolve relatively easily in water, especially acid water, and natural rain water is slightly acid

oxides

These are based on the oxygen anion, O2-. Examples include iron oxides such as hematite, Fe2O3 and magnetite, Fe3O4, and pyrolusite, MgO

sulfides

These are based on the sulfide ion, S2-. Examples include pyrite, FeS2, galena, PbS, and sphalerite, ZnS in its pure zinc form. Some sulfides are mined as sources of such metals as zinc, lead, copper, and tin

halides

These have a halogen element as the anion, whether it be fluoride, F-, chloride, Cl-, bromide, Br-, iodide, I-, or astatide, At-. Halite, NaCl, is a halide mineral

phosphates

These have the polyatomic phosphate ion, (PO4)3-, as the anion. Fluorapatite, Ca5(PO4)3F, which makes your teeth hard, is a phosphate mineral

sulfates

These have the polyatomic sulfate ion, (SO4)2-, as the anion. Anhydrite, CaSO4, is a sulfate

native elements

This is an interesting group of MINERALS.Studying native elements reminds us of the differences between the terms mineral and element.ALL minerals are made up of elements, but not all elements are minerals.Sounds like a riddle! But it's not.There are literally THOUSANDS of minerals, yet only 92 naturally occurring elements. To clarify, some minerals are merely a single element- examples being Gold (Au), native copper (Cu), and diamond and graphite (both C, carbon).Pure elements, found in nature as solids are called native elements! So, just because an element has been purified and crystallized in a laboratory doesn't qualify it as a mineral. Minerals are naturally occurring.Examples- Al and Si are present in lots of rocks, but these are not minerals.Aluminum was not isolated in a laboratory (from Al-oxides) until around 1825!Silicon was not isolated in a laboratory until around 1823.Furthermore, oxygen (O2) is common in our atmosphere (about 20%), and because it is reactive, it's also common in many rocks... but it is NOT a mineral, inasmuch as it is not found as pure elemental oxygen in solid form and in nature. We could get tricky and fancy here- I suppose that on Neptune, in the far cold reaches of our solar system, an element like oxygen might occur in pure form as a solid, but that's stretching things!

Mid-Ocean Ridges

Volcanoes erupt at mid-ocean ridges, such as the Mid-Atlantic ridge, where seafloor spreading creates new seafloor in the rift valleys. Where a hotspot is located along the ridge, such as at Iceland, volcanoes grow high enough to create islands

When a soil has equal parts of sand, silt and clay, what type of soil is present?

a leam soil

Most hotspots are__________.

basaltic

Mechanical weathering

breaks rock into smaller pieces. The rock has changed physically without changing its composition. The smaller pieces have the same minerals, in just the same proportions as the original rock

Which of the following is NOT a class of minerals?

chlorinates

Of all the different types of volcanoes, this one is the most common and are often found near larger volcanoes?

cinder cone

The tendency of a mineral to break along certain planes to make smooth surfaces is called what?

cleavage

Which type of volcano erupts with the most force?

composite

Which type of boundary are most volcanoes associated with?

convergent

Which type of boundary is associated with new seafloor being created?

divergent

Which of the following can trigger a landslide?

excessive rains

What building block of matter has either a positive or negative charge?

ion

The periodic table provides a lot of information. Which of the following is NOT provided by the periodic table?

isotope number

minerals

made of atoms (have an impact on the behavior and characteristics of the mineral)

Hydrolysis

name of the chemical reaction between a chemical compound and water. When this reaction takes place, water dissolves ions from the mineral and carries them away. These elements have undergone leaching. Through hydrolysis, a mineral such as potassium feldspar is leached of potassium and changed into a clay mineral. Clay minerals are more stable at the Earth's surface

Which of the following is not a gas commonly found in pyroclastic flow?

nitrogen dioxide

The soil type laterite is ________.

often found in hot, wet climates, and lacks nutrients

Put the following in order of their abundance, starting with the MOST abundant: carbon, silicon, oxygen, iron, and hydrogen.

oxygen, silicon, iron, hydrogen, and carbon

Which two elements are the scarcest in the crust?

potassium and magnesium

The nucleus is composed of which two subatomic particles?

protons and neutrons

mineralogists

scientists who study minerals. One of the things mineralogists must do is identify and categorize minerals. While a mineralogist might use a high-powered microscope to identify some minerals, most are recognizable using physical properties

Which type of volcano is the largest but not necessarily the most eruptive?

shield

These minerals commonly form chains, sheets, and rings?

silicates

Which element comprises about 27% of the crust?

silicon

Which of the following is a slow moving form of mass wasting?

slumps

mineralogy

study of minerals IMPORTANT: some minerals considered resources we use, such as gypsum, but they are the basis for the formation of rocks. Minerals are classified in different ways based on the elements that they contain. Matter (elements) makes up the minerals and minerals make up rocks. We can't understand rocks and rock forming process or some of the other areas of geology until we have a basic knowledge of minerals

Ice wedging

the main form of mechanical weathering in any climate that regularly cycles above and below the freezing point (figure 2). Ice wedging works quickly in both polar regions and mid-latitudes, and of course also in mountainous locations

hardness

the strength with which a mineral resists its surface being scraped or punctured. In working with hand samples without specialized tools, mineral hardness is specified by the Mohs hardness scale. The Mohs hardness scale is based 10 reference minerals, from talc the softest (Mohs hardness of 1), to diamond the hardest (Mohs hardness of 10). It is a relative, or nonlinear, scale. A hardness of 2.5 simply means that the mineral is harder than gypsum (Mohs hardness of 2) and softer than calcite (Mohs hardness of 3). To compare the hardness of two minerals see which mineral scratches the surface of the other

Lahars and pyroclastic flows both have what in common?

they are both composed of gas

Which of these soil horizons contains the greatest amount of organic matter?

topsoil

Pyroclastic flow can be composed of all but which of the following?

water