Chapter 2: Atoms, Elements, and Minerals

Double chain silicates

form when two single chains of tetrahedra link to each other by sharing oxygen atoms -A double-chain silicate is essentially two adjacent single chains that are sharing oxygen atoms. The amphibole group is characterized by two parallel chains in which every other tetrahedron shares an oxygen atom with the adjacent chain's tetrahedron. In even a small amphibole crystal, millions of parallel double chains are bonded together by positively charged ions

Single chain silicates

forms when two of a tetrahedron's oxygen atoms are shared with adjacent tetrahedra to form a chain -the ratio of silicon to oxygen is 1:3; therefore, each mineral in this group (the pyroxene group) incorporates SiO3 - 2 in its formula, and it must be electrically balanced by the positive ions (e.g., Mg + 2 ) that hold the parallel chains together. If a pyroxene has magnesium as the + 2 ions bonding the chains, it has a formula of MgSiO3 (commonly written as Mg2Si2O6 ).

stable isotopes

isotopes that do not change or decay over time -used in geology for ancient climate change studies -More C-12 in organic matter, more C-13 in atmosphere -Oxygen-18 sinks to the oceanfloor during icehouse times, so without oxygen, organic matter was preserved during greenhouse times

sulfates

minerals that contain sulfur and oxygen -ex:SO4(-2)

unstable/radioactive isotopes

nucleus decays spontaneously and gives off particles and energy -Isotopes that change or decay over time -used in geology to date igneous rock C-14 used to date organic matter younger than 50,000 years -C-14 changes to N-14 + electrons in the span of 50,000 yrs, so by measuring how much C-14 is left we can tell how much time has passed

8 most abundant elements of earth's crust

oxygen, silicon, aluminum, iron, calcium, sodium, potassium, magnesium -o.s.a.i.c.s. p.m. --mnemonic: think of a m[osaics] in the night time (pm) -In order of most abundant to least abundant -Collectively, the eight elements listed account for more than 98% of the weight of the crust -most rocks are composed largely of oxygen because it is the most abundant element in the Earth's crust

covalent bonding

sharing of electrons -bonding in which adjacent atoms share electrons

Exsolution Lamellae

similar to striations, these are thin discontinuous layers of Plagioclase within K-feldspar -lines perpendicular to mineral

Tenacity

the manner in which a substance resists breakage (bridle, malleable, elastic, sectile)

Piezoelectricity

the property of a crystal that causes it to bend or deform, producing electric vibrations, when a voltage is applied across it -Quartz can generate electricity when squeezed in a certain direction

Mineralogy

the study of minerals

ionic bonding

transfer of electrons -Atoms with different charges are attracted to one another, and this forms the basis for ionic bonding . -Ionic bonding is the most common type of bonding in minerals

Van der Waals bonds

weak electrostatic force between layers of covalently bonded molecules -weak electrostatic bond -Graphite is used in pencils and as a lubricant. Amazingly, the hardest mineral and one of the softest have the same composition. The distinction is in the bonding. In diamond, the covalent bonds form a three-dimensional structure. In graphite, the covalent bonds form sheets that are held together by much weaker electrostatic bonds (known as van der Waals bonds). It is these weak bonds that make graphite so soft

Hardness

• Hardness is a measure of resistance to scratching -The property of scratchability, or hardness , can be tested fairly reliably • A harder substance will scratch a softer one, but a softer one cannot scratch a harder one

Clarity as a physical property

• Mineral crystals also vary in their clarity (clearness, or ability to transmit light) - Transparent (clear and see-through, like glass) - Translucent (foggy, like a steamed-up shower door) - Opaque (impervious to light, like concrete and metals)

Streak

• Streak is the color of a substance after it has been ground to a fine powder. • To obtain a powder, the easiest way is to scratch a mineral on a porcelain streak plate • The color of the powder is its streak • Sometimes, the color of the mineral and the color of the streak are different • If the mineral is harder than the streak plate, it will scratch the plate and not leave a streak - in this case, you can crush a tiny piece with a hammer, or record the streak as unknown - in the end, all minerals have a streak, even if you do not see one on a streak plate

Luster

• The quality and intensity of light reflected from the surface of a mineral is called its luster • Luster cannot always be seen in a photograph:you need to have the mineral in your hands • Luster of a mineral is described by comparing it to familiar substances -Luster is either Metallic or Nonmetallic

Fracture

•If cleavage is absent, the mineral has a fracture • Fracture refers to any break in a mineral that does not occur along a cleavage plane - light is reflected randomly

Fractures can be described as:

- Conchoidal (like glass, with ribbed, smoothly curved surfaces) - Uneven (rough) - Hackly (having jagged edges) - Splintery (like splintered wood) - Fibrous (showing fiber-like structures)

Metallic luster (M)

- Metallic luster (M) occurs when minerals reflect light "like a metal" -Sometimes, metallic minerals will tarnish or weather to a nonmetallic luster: you should always observe a freshly broken surface of a mineral to determine luster • Sometimes a mineral looks submetallic. For identification purposes, it should be treated as metallic • Metallic objects can vary from bright to dull - Bright could be very reflective, shiny, polished - Dull is not very reflective, not very shiny, not very polished

Clay minerals that swell

-Clay minerals are very common at Earth's surface; they are a major component of soil -What they all have in common is that they are sheet silicates. -Montmorillonite is one of the more interesting clay minerals. It is better known as expansive clay or swelling clay. If water is added to the montmorillonite, the water molecules are adsorbed into the spaces between silicate layers. This results in a large increase in volume, sometimes up to several hundred percent. -The pressure generated by the swelling can be up to 50,000 kilograms per square meter. This is sufficient to lift a goodsized building.

Color as a physical property

-Color is easy to notice, but is often not reliable as a property. -Some minerals present varieties, different forms or colors, so other properties must be observed to identify it. -Most minerals also present a color on a freshly broken surface, and a different color on a tarnished or weathered surface (ex:oxide)

Feldspars

-Framework silicates -O/Si = 2 --felsic - Feldspars • Ca-Plagioclase • Na-Plagioclase • K-Feldspar • Quartz

olivine

-Isolated tetrahedra -O/Si= 4 -Mafic -contains two ions of either magnesium (Mg + 2 ) or iron (Fe + 2 ) for each silicon- oxygen tetrahedron

Micas

-Sheet silicates -O/Si= 2.5 • Biotite (mafic) • Muscovite (felsic)

Cleavage

-The internal order of a crystal may be expressed externally by crystal faces, or it may be indicated by the mineral's tendency to split apart along certain preferred directions. Cleavage is the ability of a mineral to break, when struck or split, along preferred planar directions • Cleavage is the tendency of some minerals to break (cleave) along flat, parallel surfaces • Do not confuse cleavage with crystal habit, cleavage relates to how a crystal breaks • Cleavage planes are parallel surfaces of weak chemical bonds • More than one set of of cleavage planes can be present • Each set constitutes a cleavage direction, minerals are characterized by one, two, or more cleavage directions • Cleavage can be excellent, good, poor, or absent. Excellent cleavage - light is reflected in one direction from a set of large parallel surfaces • Good cleavage - light is reflected in one direction from a set of many small parallel surfaces • Poor cleavage - light is reflected from a set of small flat parallel surfaces difficult to detect

Silicates

-Type of mineral group - contain silica (SiO2), O combined with Si - O and Si are the most common elements in the Crust - The most common minerals are silicates, which incorporate the most abundant elements on Earth - Silicates are the most common group of minerals in the Earth's Crust -All different kinds of silicates are built with the same basic unit, which is the Silicon Tetrahedron -Most silicate minerals also contain one or more other elements.

Formula of Halite

-aka salt -a mineral -NaCl

amphiboles

-double chain --O/Si= 3 -Mafic

Crystal Habit

-refers to the general crystal form(s)and combination(s) in which a mineral habitually forms.

Pyroxenes

-single-chain silicate minerals -O/Si= 3 -Mafic

Striations

-straight, parallel lines on the flat surfaces of crystal faces -Long parallel scars in rocks carved by rock fragments being dragged across them by a glacier (erosional) -"hairline" grooves on the cleavage surface of some minerals (typical of K-feldspar)

Crystal Form

-the geometric shape of a crystal -The crystal form of a mineral is a set of faces that have a definite geometric relationship to one another -Each specific crystal form can be classified into one of six crystal systems, according to the number, length, and angular relationships of imaginary geometric axes along which its crystal faces grew • Crystal form is an external feature of mineral crystals. Perfect crystals can only develop if a mineral crystal is unrestricted as it grows. • This is rare. When crystals grow together (they are intergrown). Once they touch each other, they stop growing & they do no exhibit their crystal form. • Most crystalline rocks show intergrown patterns

Partial melting

-the process by which different minerals in rock melt at different temperatures -magma that is more felsic rises first

compositional zoning

-when a mineral changes composition as it grows during cooling -centers of crystals have mostly 1 type of cation and rims have another -Calcium-rich plagioclase is more stable at the high temperatures in which the crystals start growing. The crystals then develop sodium-rich rims as the remaining melt crystallizes.

Types of Silicates

1) Isolated Silicate Structure (tetrahedra are not connected) 2) Single chain silicates (tetrahedra connected to form single chains) 3) Double chain silicates (tetrahedra connected to form double chains) 4) Sheet silicates (tetrahedra connected to form flat sheets) 5) Framework silicates (tetrahedra connected in all directions)

Cation

A cation is a positively charged ion that has fewer electrons than protons

Law of Constancy of Interfacial Angles

A law which states that the angle between equivalent faces of the same mineral is always the same -a Danish naturalist of the seventeenth century, first noted that the angle between two adjacent faces of quartz is always exactly the same, no matter what part of the world the quartz sample comes from or the color or size of the quartz

Mineral

A mineral is a naturally occurring, inorganic, crystalline solid that has a specific chemical composition, and has distinctive physical properties -Must be a solid, cannot be a liquid or gas -Naturally occurring tells us that a mineral must form through natural geologic processes -Inorganic means that minerals are not composed of the complex hydrocarbon molecules that are the basis of life-forms such as humans and plants -Minerals have a specific chemical composition that can be described by a chemical formula. Chemical formulas tell you which elements are in the mineral and in what proportion. -All minerals have a crystalline structure where the atoms that make up the mineral are arranged in an orderly, repeating, three-dimensional pattern -Physical properties include: Density, gravity, magnetism, melting/boiling point -Minerals are composed of elements bonded together in an orderly crystalline structure -Bonds help minerals stay together

Mohs hardness scale

A scale ranking ten minerals from softest to hardest; used in testing the hardness of minerals • Mohs developed a quantitative scale of relative mineral hardness • In the Mohs scale, the softest mineral (Talc) has a hardness of 1, and the hardest mineral (Diamond) has a hardness of 10 • A piece of glass has a hardness of 5.5 • Glass is used as a reference to distinguish between hard and soft minerals • If the mineral scratches the glass, it is hard • If the mineral cannot scratch the glass, it is soft

anion

An anion is a negatively charged ion that has more electrons than protons

Formula of quartz

SiO2 (silica) --a mineral

specific gravity (SG)

The ratio of density of a mineral divided by density of water -S.G = Density of mineral (ing/cm^3) / Density of water(in g/cm^3) -the units cancel out so there is no units • For instance, what is the Specific Gravity of Copper Cu, when its density is 9g/cm3? • SG Copper = D Cu / DH2O = 9g/cm3 / 1g/cm3 = 9

Oxygen isotopes and climate change

Water that evaporates or is respirated by plants or animals will have a slightly higher abundance of the lighter isotope ( 16 O) relative to the heavier isotope (18 O) than the water left behind. Colder water will have a higher ratio of 18 O to 16 O than warmer water. -Oxygen isotope studies have allowed scientists to identify climate changes during relatively recent geologic time by determining the temperature changes of ocean water -Because we cannot sample past oceans, we use fossil shells to determine the oxygen isotope ratios at the time the organisms were alive. -While they are alive, they grow their shells of calcite (CaCO 3 ), incorporating oxygen from the seawater. The oxygen in the shells has the 18 O/ 16 O ratio that is the same as that of the seawater. The particular isotopic ratio reflects the temperature of the seawater -When foraminifera die, their shells settle onto the deep ocean floor, where they form a thin layer upon older layers of tiny shells. Deep-sea drilling retrieves cores of these layers of sediment. Foraminifera from each layer are analyzed and the 18 O/ 16 O ratios determined. The ages of the layers are also determined. From these data, the temperature of the ocean's surface water is inferred for the times the foraminifera were alive.

Sulfides

compounds that consist of one or more elements combined with sulfur -Sulfides have S but not O in their formulas -FeS2

Sheet silicates

form when each tetrahedron shares three of its oxygen atoms with other tetrahedra -In a sheet silicate structure , each tetrahedron shares three oxygen atoms to form a sheet. The mica group and the clay group of minerals are sheet silicates. The positive ions that hold the sheets together are sandwiched between the silicate sheets

Element

An element is defined by the number of protons in its nucleus or its atomic number. -For example, oxygen has an atomic number of 8, which tells you that it has eight protons -Minerals are made of elements

Ion

An ion is an atom that has a surplus or deficit of electrons relative to the number of protons in its nucleus and therefore a positive or negative electrical charge

atomic weight/mass

Atomic weight , or atomic mass , is the weight of an average atom of an element, given in atomic mass units. Because sodium has only one naturally occurring isotope, its atomic mass number and its atomic weight are the same—23. On the other hand, chlorine has two common isotopes, with mass numbers of 35 and 37. The atomic weight of chlorine, which takes into account the abundance of each isotope, is 35.5 because the lighter isotope is more common than the heavier one.

Atoms

Atoms are the smallest, electrically neutral assemblies of energy and matter that we know exist in the universe

nucleus

Atoms consist of a central nucleus surrounded by a cloud of electrons. The nucleus contains positively charged protons and neutral particles called neutrons . Surrounding the nucleus is a cloud of negatively charged electrons

Formula of Calcite

CaCO3 --a mineral

Eons since 4600 my to 0 my

Hadean (4600-4000) mya Archean (4000-2500) mya Proterozoic (2500-590) mya Phanerozoic (590-0) mya

polarity of water molecules

In a water molecule, the two hydrogen atoms are covalently bonded tightly to the oxygen atom. However, the shape of the molecule is asymmetrical, with the two hydrogen atoms on the same side of the atom. This means the molecule is polarized, with a slight excess positive charge at the hydrogen side of the molecule and a slight excess negative charge at the opposite side -When water is in its liquid state, the molecules are moving about. Because of the polarity, molecules are slightly attracted to one another. For this reason, water molecules are closer together than molecules in most other liquids. However, in ice the water molecules are not as tightly packed together as in liquid water.

solid solution series

Ions of like size and charge may freely substitute for one another in the atomic structures of minerals. Iron (Fe 2+ ) and magnesium (Mg 2+ ), for example, interchangeably substitute to create a range of compositions in the common silicate mineral olivine. This is represented by the parentheses in the formula of olivine—(Mg,Fe)2 SiO4. Olivine is an example of a solid solution series, with pure magnesium olivine, Mg2SiO4, forming the bright green variety forsterite (or peridot, as a gem), and pure iron olivine forming the jet black variety fayalite, Fe2SiO4 . The crystal structures of forsterite and fayalite are virtually identical

Isotopes

Isotopes of an element are atoms containing different numbers of neutrons but the same number of protons. -Isotopes are either stable or unstable. An unstable, or radioactive, isotope is one in which protons or neutrons are, over time, spontaneously lost or gained by the nucleus

nonmetallic luster

Luster that gives a substance the appearance of being made of something other than metal (e.g., glassy). -- Nonmetallic luster (NM) occurs in all other minerals -Nonmetallic luster is more common •Nonmetallic luster can also be described with more specific terms: - Vitreous (glassy or glazed looking) - Waxy - Pearly - Satiny - Earthy (resembles the surface of unglazed pottery and is characteristic of the various clay minerals) - Greasy - Porcelaneous

Chemical formula of Olivine

Mg2SiO4 or Fe2SiO4

Oxides

Minerals containing oxygen and a metal -that is, it contains oxygen not bonded to Si, C, or S

carbonates

Minerals that contain the elements carbon, oxygen, and one or more other metallic elements -The carbonates have CO3 in their formulas. Calcite, CaCO3 , is a member of this group and is one of the most abundant minerals at the Earth's surface where it occurs mainly in the sedimentary rock limestone

polymorphs

Minerals with the same composition but different crystalline structures -ex diamond and graphite are both made of carbon

Native elements

Native elements have only one element in their formulas. Some examples are gold (Au), copper (Cu), and the two minerals that are composed of pure carbon (C), diamond and graphite.

Order of minerals in silicates

Olivine, Pyroxenes, Amphiboles, Biotite Muscovite, Ca-Plagioclase, Na-Plagioclase, K-Feldspar, Quartz -Possible mnemonic??: OPA BM CN KQ Think OPAl, BabyMomma, Cartoon Network, Korean bbQ

Other Physical Properties

Other Physical Properties a. Tenacity b. Reaction with Acid c. Magnetism d. Striations e. Exsolution Lamellae f. Specific Gravity g. Piezoelectricity h. Double refraction

Phanerozoic eras

Paleozoic (590-250) mya Mesozoic (250- 66.5) mya Cenozoic (66.5- 0) mya

Physical Properties of Minerals: Seven Common Properties

Physical Properties of Minerals: Seven Common Properties 1. Color and Clarity 2. Crystal Habits and Forms 3. Luster 4. Streak 5. Hardness 6. Cleavage 7. Fractures

Rock

Rocks are defined as naturally formed aggregates of minerals or mineral-like substances -A rock can be composed of a single mineral, it is still an aggregate of many mineral grains. -Some rocks can be composed of non-mineral substances (ex:coal is made of partially decomposed organic matter, & obsidian which is volcanic glass) -Most rocks are formed by about 20 minerals

Precipitates

Silicate minerals such as quartz, olivine, and the feldspars (plagioclase and potassium feldspar) crystallize primarily from molten rock (magma). They are precipitates— products of crystallizing liquid. Other precipitates include the carbonates calcite and aragonite, which grow in spring and cave waters and precipitate from ocean water. -Some minerals precipitate due to evaporation (e.g., halite). -Some minerals result from biological activity; for example, the building of coral reefs creates huge masses of calcite-rich limestone. -Some minerals crystallize directly from volcanic gases around volcanic vents—a process termed sublimation. Examples include ordinary sulfur

Isolated Silicate Structure

Silicate minerals that are structured so that none of the oxygen atoms are shared by silica tetrahedrons. - The individual silicon-oxygen tetrahedra are bonded together by positively charged ions -ex:Olivine

ionic radius

The "size" of an atom (or an ion) is essentially the radius of its electron field -Ionic radii play an important role in the arrangement of atoms in a crystalline structure as well --When ions come together they tend to pack as efficiently as possible. No irregular holes may exist in the arrangement. A large number of anions (negatively charged ions) may crowd around a single, large cation (positively charged ion), while only a few anions may cluster about a small cation -The ions that are close in size are in the same row, and these can replace one another in a crystal structure -ex:Halite; The alternating three-dimensional stacking of atoms creates a box-like grid that is expressed in the cubic form of halite crystals

Oxidation Number, or Valence

The Oxidation Number of an atom represents how many electrons would be needed to have a complete, stable electronic structure • It determines the kind of chemical bond • It determines who is bonding with who • In a mineral, the sum of oxidation number must be zero

atomic mass number

The atomic mass number is the total number of neutrons and protons in an atom. Compared to protons and neutrons, electrons are so tiny that their mass does not contribute to the atomic mass of the atom

Magnetism

The force of attraction or repulsion of magnetic materials -some minerals will be attracted to a magnet

Framework silicates

When all four oxygen ions are shared by adjacent tetrahedra, a framework silicate structure is formed -Quartz, feldspars

Hydrogen bonding in water

When water freezes, positive ends of the water molecules are attracted to negative ends of adjacent water molecules. (This type of bonding is known as hydrogen bonding). The result is an orderly, three-dimensional pattern that is hexagonal,as in a honeycomb (which explains the hexagonal shape of snowflakes).The openness of the honeycomb like, crystalline structure of ice contrasts with the more closely packed molecules in liquid water. This is the reason ice is less dense than liquid water. This is an unusual solid-liquid relationship. For most substances, the solid is denser than its liquid phase. -The fact that ice is less dense than liquid water has profound implications. Ice floats rather than sinks in liquid water. -The Arctic Ocean surface freezes during the winter but only at its surface. If the ice were to sink, more ocean water would be exposed to the cold atmosphere and would freeze and sink -Eventually,the entire Arctic Ocean would freeze and would not thaw during the summer. If this were the case, life, as we know it, probably would not exist.

metallic bonding

a bond formed by the attraction between positively charged metal ions and the electrons around them -is found in metals, such as copper or gold. - The atoms are closely packed, and the electrons move freely throughout the crystal so as to hold the atoms together. The ease with which electrons move accounts for the high electrical conductivity of metals. -electrons are free to move throughout the crystals

silica

a material found in magma that is formed from the elements oxygen and silicon -Silica is a term for oxygen combined with silicon. -Because silicon is the second most abundant element in the crust, most minerals contain silica. -The common mineral quartz (SiO2 ) is pure silica that has crystallized.

nonsilicate minerals

a mineral that does not contain compounds of silicon and oxygen -not as abundant in Earth -Includes: Carbonates (contain carbonate ion CO3), Sulfides (contain S), Sulfates (contain sulfate ion SO4), Oxides (contain O but not with C,S, or Si), Chlorides (contain Cl),

Double refraction

a special property of minerals in which light is bent causing an image to be doubled -A clear crystal of calcite exhibits an unusual optical property. If you place transparent calcite over an image on paper, you will see two images -Calcite crystals can split light into two components

Silicon Tetrahedron

a structure composed of four oxygen atoms (anions) surrounding a much smaller silicon atom that constitutes the basic building block of silicate minerals -tetra=4; hedron=sides -The four-sided, pyramidal, geometric shape called a tetrahedron is used to represent the four oxygen atoms surrounding a silicon atom. Each corner of the tetrahedron represents the center of an oxygen atom -Silicon and oxygen combine to form the atomic framework for most common minerals on Earth. -Within a silicon-oxygen tetrahedron, the negative charges exceed the positive charges -A single silicon-oxygen tetrahedron is a complex ion with a formula of SiO4 (-4) because silicon has a charge of + 4, and the four oxygen ions have eight negative charges ( - 2 for each oxygen atom). -For the silicon-oxygen tetrahedron to be stable within a crystal structure, it must either (1) be balanced by enough positively charged ions or (2) share oxygen atoms with adjacent tetrahedra and therefore reduce the need for extra, positively charged ions. -The structures of silicate minerals range from an isolated silicate structure, which depends entirely on positively charged ions to hold the tetrahedra together, to framework silicates (quartz, for example), in which all oxygen atoms are shared by adjacent tetrahedra