Chapter 3 + 4 Study Guide

luster

The way a mineral reflects light

Write a statement describing how magmatic differentiation can result in the formation of one or more secondary magmas from a single parent magma

-magmatic differentiation is the formation of one or more secondary magmas from a single parent magma - At any stage in the evolution of a magma, the solid and liquid components can separate into two chemically distinct units. Furthermore, magmatic differentiation within the secondary magma can generate other chemically distinct masses of molten rock.

List the properties that are used in mineral identification and briefly describe each.

1. A mineral's luster is the manner in which light reflects from the mineral's surface. 2. The color of a mineral can be ambiguous or misleading due to even slight impurities that impart a variety of possible colors to the mineral. One such example is quartz, which occurs in a variety of colors related to different impurities. 3. Due to the result of breaking along planes of weak atomic bonding, cleavage produces relatively smooth, flat surfaces. In contrast, fracture occurs when atomic bonds are more equally strong in all directions resulting in a more randomly uneven broken surface. 4. Tenacity describes a mineral's resistance to deformation like breaking, bending, or cutting. Terms that describe mineral tenacity are malleable, sectile, and elastic. 5. The effervescent reaction with cold, dilute hydrochloric acid is the simple test to confirm the identification of the mineral calcite.

Compare and contrast these intrusive igneous structures: dikes, sills, batholiths, stocks, and laccoliths.

1. As magma rises through the crust, it displaces the preexisting crustal rocks which are referred to as the "country rock" or "host rock." 2. Dikes are tabular, discordant intrusive rock bodies that cut across the structures of the country rock. Sills are tabular, concordant intrusive rock bodies that are squeezed into the weaknesses between sedimentary beds or horizontal structures of the country rock. 3. Batholiths are massive, discordant plutonic bodies. They are the largest plutons with a surface exposure greater than 100 km2. Stocks are similar to batholiths but with a much smaller surface area, less than 100 km2. Laccoliths are also considered massive plutons, but they are concordant rather than discordant, meaning they do not cut across the sedimentary layers they are intruding. Laccoliths form by arching sedimentary layers upward to allow more intrusive material to accumulate without becoming discordant.

Compare and contrast the four basic igneous compositions: basaltic (mafic), granitic (felsic), andesitic (intermediate), and ultramafic.

1. Oxygen and silicon being the most abundant elements in Earth's crust, igneous rocks are composed mainly of silicate group minerals. 2. Light-colored igneous rocks are composed mainly of nonferromagnesian silicate minerals (dominantly light-colored feldspars and quartz) with a minor amount (10 to 20 percent) of the ferromagnesian silicates. Dark-colored igneous rocks are composed primarily of dark- colored ferromagnesian silicates and calcium-rich plagioclase. 3. Felsic (granitic) igneous rocks are composed mainly of nonferromagnesian silicate minerals (dominantly light-colored feldspars and quartz) with a minor amount (10 to 20 percent) of the ferromagnesian silicates. Intermediate (andesitic) rocks contain more of the ferromagnesian minerals (30 to 50 percent) and little or no quartz. In contrast, the dark- colored mafic (basaltic) igneous rocks are dominantly made of ferromagnesian silicates (60 to 80 percent or more) and the gray, calcium-rich plagioclase feldspar. The ultramafic rocks are composed primarily of the ferromagnesian minerals olivine and pyroxene with little or no calcium-rich plagioclase feldspar. 4. The felsic igneous rocks have the highest silica content and also the highest potassium, aluminum, and sodium, but contain relatively little iron, magnesium, and calcium. In comparison, as silica content decreases in the more mafic rocks, iron, magnesium, and calcium content increases. The silica content affects the viscosity of the magma. With more silica, the magma becomes more viscous and so moves more sluggishly. With lower silica content, magmas become more fluid and flow more easily.

pluton

A body of magma that has hardened underground

covalent bond

A chemical bond that involves sharing a pair of electrons between atoms in a molecule

pegmatite

A light (felsic) igneous rock that is very coarse-grained.

viscosity

A liquid's resistance to flowing

hardness

A measure of how easily a mineral can be scratched

Cleavage

A mineral's ability to split easily along flat surfaces.

magma

A molten mixture of rock-forming substances, gases, and water from the mantle

crystal settling

A process that occurs when the earlier-formed minerals are denser than the liquid portion and sink to the bottom of the magma chamber.

mohs hardness

A scale ranking ten minerals from softest to hardest; used in testing the hardness of minerals

dike

A slab of volcanic rock formed when magma forces itself across rock layers

Mineral

A solid inorganic substance of natural occurrence.

Identify and describe the six major igneous textures.

Aphanitic (a = not, phaner = visible) rocks in contrast to phaneritic rocks, typically form from lava which crystallize rapidly on or near Earth' surface. The individual crystals in an aphanitic igneous rock are not distinguishable to the naked eye. 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. Pegmatitic texture occurs during magma cooling when some minerals may grow so large that they become massive. Phaneritic (phaner = visible) textures are typical of intrusive igneous rocks, these rocks crystallized slowly below Earth's surface. Porphyritic textures develop when conditions during cooling of a magma change relatively quickly. 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

Ionic bond

Formed when one or more electrons are transferred from one atom to another. The electrostatic attraction that binds oppositely charged ions together.

magmatic differentiation

Fractional crystallization is the removal and segregation from a melt of mineral precipitates; except in special cases, removal of the crystals changes the composition of the magma

Distinguish among the common igneous rocks based on texture and mineral composition.

Igneous rocks can be classified by composition based on the major minerals in the rocks. Light colored rocks have granitic compositions. Dark-colored rocks have basaltic compositions. Dark-colored rocks that contain only olivine and pyroxene are ultramafic.

Distinguish between ionic bonds, covalent bonds, hydrogen bonds* and metallic bonds.

Ionic Bonds: one atom gives up one or more of its valence electrons to another atom to form ions— positively and nega-tively charged atoms. The atom that loses electrons becomes a positive ion, and the atom that gains electrons becomes a negative ion. Oppositely charged ions are strongly attracted to one another and join to form ionic compounds. Covalent Bonds: The strong attractive force that holds two hydrogen atoms together results from a covalent bond, a chemical bond formed by the sharing of a pair of electrons between atoms. Metallic Bonds: A few minerals, such as native gold, silver, and copper, are made entirely of metal atoms that are packed tightly together in an orderly way. The bonding that holds these atoms together is the result of each atom contributing its valence electrons to a common pool of electrons that are free to move throughout the entire metallic structure. The contribution of one or more valence electrons leaves an array of positive ions immersed in a " sea" of valence electrons.

felsic composition

Light silicates that are rich in silica that contain quartz and feldspar

Describe how partial melting of the mantle rock peridotite generates basaltic (mafic) magma.

Magma forms by partial melting of upper mantle and crust. Partial melt means that only a fraction of the available material forms a melt, and that the remainder stays solid. The partial melt rises because of its lower density and ascends through the crust. The reason why the mantle and crust can form partial melts is because they consist of several (minerals).

lava

Magma that reaches Earth's surface

non-silicate

Minerals that do not have a combo of silicon and oxygen.

Distinguish between compositional and structural variations in minerals and give examples.

Most minerals contain impurities and several also display ionic substitution. There are other minerals which have identical chemical compositions, but different crystalline structures due to the conditions under which they crystallized. A. Impurities - Most minerals have non-structural ions trapped or included in the atomic structure during growth of the structure. B. Ionic Substitution - variations in composition resulting from a systematic substitution of ions - There are several minerals which display solid solution (solids which act like solutions during crystallization and melting). The olivine group, forsterite (Mg2SiO4) - fayalite (Fe2SiO4) is a good example. Both Mg+2 and Fe+2 have the same charge (+2) and about the same ionic size so that either can fit into the olivine crystalline structure. Coupled Ion Substitution - the plagioclase series - NaAlSi3O8 to CaAl2Si2O8 is an example of a solid solution with coupled ion substitution - The ions don't have the same charge, but are able to substitute for one another when coupled with another ion. Within the plagioclase crystal structure, Ca+2and Al+3 with a combined charge of +5 substitute for Na+1 and Si+4 which also have a combined charge of +5. C. Polymorphs - minerals which have the identical chemical composition, but different internal structure - The best examples are the carbon polymorphs, diamond and graphite, which are both composed of pure carbon but have substantial differences in their atomic packing and bonding.

List the common non-silicate minerals and explain why each is important.

Oxides contain oxygen as the anion. These minerals include corundum, hematite, magnetite, chromite and limenite. Corundum is one of the hardest substances known to humanity and is made of aluminum and oxygen. Gems of corundum include rubies and sapphires. Hematite and magnetite are iron ores. Sulfides and sulfates both contain sulfur; the difference is that sulfates also contain oxygen bound to sulfur, whereas sulfides just contain sulfur atoms. Pyrite, galena, chalcopyrite and bornite contain sulfides. Sulfates include gypsum, anhydrite and barite. Carbonate minerals consist of carbon and oxygen atoms as anions. Calcite, dolomite, malchite and azurite are common carbonates. Some of these minerals produce bubbles when hydrochloric acid touches them. Phosphates consist of phosphorous bound to oxygen atoms. Apatite and turquoise are two common phosphate minerals. Halide minerals contain fluorine or chlorine. Halite, or salt, is one of the most common halide minerals in the Earth. Fluorite and sylvite also contain halide gases.

Compare and contrast the three primary particles contained in atoms.

Protons: positively charged, mass 1 (elements are defined by number of protons. Neutrons: no charge, mass 1 atomic mass is (#protons + #neutrons) Electrons: negative charge, negligible mass

ultramafic composition

Rare composition that is high in magnesium and iron

bowen's reaction series

Shows the order of mineral crystallization and composition of rocks

silicate

SiO4 -2, four oxygen joined to one silicon atom in a tetrahedron

Conchoidal fracture

Smoothly curving, clamshell-shaped surfaces along which materials with no cleavage planes tend to break

Summarize the major processes that generate magma from solid rock.

Solid rock may melt under three geologic circumstances: when heat is added to the rock, raising its temperature; when already hot rock experiences lower pressures ( de-compression, as occurs at mid- ocean ridges); and when water is added to hot rock that is near its melting point ( as occurs at subduction zones).

Octet Rule

States that atoms lose, gain or share electrons in order to acquire a full set of eight valence electrons

aphanitic

The characteristic of a rock that does not show grains (too small to see.)

valence electron

The electrons in the outermost shell (main energy level) of an atom; these are the electrons involved in forming bonds.

Compare and contrast the light (non-ferromagnesian) silicates with the dark (ferromagnesian) silicates, and list four common minerals from each group.

The main difference between the light and dark silicates is their relative specific gravities (densities); light silicates are less dense (lower specific gravity) than the dark silicates. This difference is mainly due to the amounts of iron and magnesium that are present, with light silicates containing much less iron and magnesium and relatively more potassium, aluminum, and sodium relative to the dark silicates.

Explain how minerals are classified and name the most abundant mineral group in Earth's crust.

The most abundant mineral group found in the Earth's crust is the silicate group. The silicate minerals contain both oxygen and silicon, which are also the two most abundant elements contained in the Earth's mantle. Silicates are also the most common minerals in the rock-formation process, and it has been estimated that they comprise 75 to 90 percent of the Earth's crust.

Describe three mechanisms that generate minerals and rocks.

The rotation of platy mineral grains shows that the new alignment is roughly perpendicular to the direction of maximum stress. Recrystallization that produces new minerals occur perpendicular to the direction of maximum stress. The newly formed mineral grains exhibit a distinct layering, and the metamorphic rocks containing them exhibit foliation. Flattening spherically shaped grains normally develop roughly spherical crystals and have a rather simple chemical composition.

Crystal habit

The shape in which a mineral's individual crystals or aggregates of crystals grow.

glassy

The texture of igneous rocks that cool too quickly to form crystals.

porphyritic

The texture of igneous rocks that form when slow cooled course-grained rock is erupted. The result is large crystals embedded in smaller crystals.

hydrogen bonds

Very weak bonds; occurs when a hydrogen atom in one molecule is attracted to the electrostatic atom in another molecule

metallic bond

a bond formed by the attraction between positively charged metal ions and the electrons around them

intermediate composition

a composistional group of igneous rocks indicating that the rock contains al least 25% dark silicate minerals, the other dominate mineral is plagioclase feldspar. Composite Volcanoes (Stratovolcanoes)

batholith

a mass of rock formed when a large body of magma cools inside the crust

mafic composition

a silicate mineral or igneous rock that is rich in magnesium and iron

sill

a slab of volcanic rock formed when magma squeezes between layers of rock

List and describe the three major components of magma

a. Liquid (melt)—This portion is the mobile ions mostly of the eight common elements (silicon, oxygen, aluminum, iron, calcium, sodium, potassium, and magnesium). b. Solid—This portion consists of minerals that have crystallized from the magma as it cools. c. Volatiles—This portion consists of components that would form a gas at surface pressures, but are dissolved in the magma. The most common volatile is water vapor, followed by carbon dioxide and sulfur dioxide.

phaneritic

coarse grained

streak

color of a mineral when it is in powdered form.

volatile

easily aroused or changeable; lively or explosive

polymorph

having many forms The ability of a solid material to exist in more than one form or crystal structure

Sketch the silicon—oxygen tetrahedron and explain how these fundamental building blocks join together to form the five common silicate structures.

https://www.britannica.com/science/silicon-oxygen-tetrahedron

vesicular

igneous rock texture that has air bubbles, large minerals, and forms with amino acid

List the main characteristics that an Earth material must possess to be considered a mineral, and describe each.

naturally occuring, solid substance, orderly crystalline structure, definite chemical composition, generally considered inorganic

intrusive

plutonic, a type of ingneous rock that generally contains large crystals and forms when magma cools slowly beneath Earth's surface.

assimilation

process of magmatic differentiation whereby ascending magmas evolve chemically by recruiting easily melted or dissolved components (fusibles) from the walls of their conduits.

Silicon oxygen tetrahedron

pyramid with 4 faces, 4 oxygen ions that are covalently bonded to a silicon ion

magma mixing

the process of altering the composition of a magma through the mixing of material from another magma body

extrusive

volcanic, fine-grained igneous rock that forms when magma cools quickly at or near Earth's surface

xenolith

when a different type of rock is incorporated into another plutonic rock