Geology Exam 2

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Biomineralization

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Biomineralization

Biogenic minerals, such as those in clam shells, are produced by organisms through a process called

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In the crystalline lattice of minerals,

atoms occur in a specific and repeating pattern

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Minerals can form by

-solidification of a melt -precipitation from a water solution or a gas -diffusion through a solid -metabolism of organisms

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chemical bonds in minerals

ionic, covalent, metallic, van der waals

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chemical bond

the force that holds two atoms or ions together

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ionic

-halite, sodium chloride (NaCl) -relatively weak

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ionic bond

a chemical bond resulting from the attraction between oppositely charged ions -transfers electrons

<p>a chemical bond resulting from the attraction between oppositely charged ions -transfers electrons</p>
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covalent

-diamond, carbon -very strong -shared electrons

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covalent bond

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

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metallic bond

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

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metallic

-native metals -malleable -ductile -sectile

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maleable

can be pounded into a foil; characteristic of a soft metal

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ductile

can be pulled into a wire; can be pulled and stretched

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sectile

can be cut with a knife

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native metals

-iron -gold -silver -platinum -copper -all electrically conductive

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van der waals

a slight attraction that develops between the oppositely charged regions of nearby molecules

<p>a slight attraction that develops between the oppositely charged regions of nearby molecules</p>
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properties of a mineral

-color -streak -luster -hardness -crystal habit -cleavage fracture -special properties

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color

the characteristic of a material due to the spectrum of light emitted or reflected by the material, as perceived by eyes or instruments

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streak

the color of the powder produced by pulverizing a mineral on an unglazed ceramic plate

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luster

appearance to reflection of light; the way it shines

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hardness

-a measure of the relative ability of a mineral to resist scratching -it represents the resistance of bonds in the crystal structure from being broken

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crystal habit

the general shape of a crystal or cluster of crystals that grew unimpeded

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cleavage fracture

the way a mineral breaks

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glass and porcelain have a

concoidal fracture

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chemical groups of minerals

-silicates -oxides -sulfides -sulfates -halides -carbonates -and native metals

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silicates

-most common group of minerals -minerals that contain silicon and oxygen and usually one or more other elements [SiO4]^4 SiO4 tetrahedran nesosilicates sorosilictaes

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groups of silicate minerals are distinguished from each other by the ways in which

the silicon-oxygen tetrahedra that constitute them are linked

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nesosilicates

-isolated tetrahedra -ex: olivine

<p>-isolated tetrahedra -ex: olivine</p>
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sorosilicates

-two SiO4 tetrahedra sharing a single oxygen -sister silicates

<p>-two SiO4 tetrahedra sharing a single oxygen -sister silicates</p>
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oxides

-compounds that contain oxygen and an element other than silicon -ex: aluminum oxide (Al2O3) -hematite: ore of iron

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cations of oxides

aluminum (Al), iron (Fe), titanium (Ti), etc.

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anion of oxides

oxygen (O^-2)

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sulfates

-minerals that contain sulfur and oxygen -ex: CaSO4 (calcium sulfate), gypsum, sheetrock, BaSO4 (barium sulfate)

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carbonates

-minerals that contain the elements carbon, oxygen, and one or more other metallic elements -Ca^+2[CO3]^-2; calcite -cement -lime CaO

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halides

-minerals that contain a halogen ion plus one or more other elements -halite, NaCl -flouride, CaF2

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sulfides

-compounds that consist of one or more elements combined with sulfur -ore of lead: galena (PbS) -ore of zinc: sphalerite (ZnS) -iron disulfide (FeS2)

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native elements (metallic bonds)

sulfur (S) carbon (C) (graphite and diamond) gold (Au) silver (Ag) copper (Cu) iron (Fe) platinum (Pt)

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rock cycle

the succession of events that results in the transformation of Earth materials from one rock type to another, then another, and so on

<p>the succession of events that results in the transformation of Earth materials from one rock type to another, then another, and so on</p>
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Not all atoms follow the same path through the rock cycle

For example, an igneous rock could later be eroded and turned into sediment, which could become a sedimentary rock, which might eventually be metamorphosed. Or the igneous rock could be metamorphosed directly

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The rock cycle happens because

the Earth is dynamic, and its internal and external sources of energy drive melting, uplift, faulting, weathering, erosion, and burial

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resorvoir

-a region that contains a volume of material -for example, in the context of the Earth System, the ocean is the largest reservoir of liquid water on the Earth. -in the context of discussing hydrocarbons, a porous sandstone may be a good reservoir for oil or gas.

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At the surface of the Earth, heat from the Sun, together with gravity, drives

-wind, rain, ice, and currents -these agents of weathering and erosion grind away at the surface of the Earth and send material into the sedimentary path of the cycle

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sediment

small, solid pieces of material that come from rocks or living things

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lithification

the physical and chemical processes that transform sediments into sedimentary rocks -process begins with compaction and ends in cementation

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compaction

the pressure of the overburden on the buried rock squeezes out water and air that was trapped between clasts, and the clasts press tightly together

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cementation

cement, consisting of minerals that precipitate from groundwater, partially or completely fills the spaces between clasts and attaches each grain to its neighbor

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magma

melt underground

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lava

melt that has emerged to the surface

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causes of melting

  1. decompression

  2. flux melting (addition of volatiles)

  3. heat transfer

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(melting due to decompression) because pressure prevents melting, even in a very hot rock,

a decrease in pressure can trigger melting as long as the rock remains hot

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decompression melting

-takes place where hot mantle rock rises slowly. as the rock moves up, its pressure becomes less (due to the decrease in overburden) while its temperature remains nearly unchanged (rock acts as an excellent insulator) -melting due to a drop in confining pressure that occurs as rock rises

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Magma also forms at locations where

volatiles mix with hot mantle rock

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volatiles

-gaseous components of magma dissolved in the melt -volatiles will readily vaporize (form a gas) at surface pressures -H2O and CO2

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melting due to addition of volatiles

-when volatiles mix with hot, dry rock, they react with minerals and break chemical bonds so that the rock begins to melt -a process known as flux melting

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flux melting

-when volatiles mix with hot, dry rock, they react with minerals and break chemical bonds so that the rock begins to melt -adding volatiles decreases a rock's melting temperature

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melting due to heat transfer

when very hot magma from the mantle rises into the crust, the heat it brings raises the temperature of the surrounding crustal rock

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heat transfer melting

melting that results from the transfer of heat from a hotter magma to a cooler rock

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upward movement causes decompression melting

in mantle plumes, beneath rifts, and beneath mid-ocean ridges

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extrusive (volcanic) igneous rocks

-rock that forms by the freezing of lava above ground, after it flows or explodes out (extrudes) onto the surface and comes into contact with the atmosphere or ocean -small crystals -cools/crystallizes quickly -aphanitic

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intrusive (plutonic) igneous rock

rock formed by the freezing of magma underground -large crystals -cools/crystallizes slowly -phaneritic

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aphanitic

an igneous rock that contains crystals so small one can't see them without a microscope

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phaneritic

an igneous rock that contains crystals that the naked eye can see

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porphyritic texture

an igneous rock texture in which large crystals are scattered on a background of much smaller crystals.

<p>an igneous rock texture in which large crystals are scattered on a background of much smaller crystals.</p>
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porphyritic rocks

have larger crystals (called phenocrysts) surrounded by a mass of fine crystals (called groundmass)

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phenocrysts

large crystals in porphyritic rocks

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porphyritic rocks form when a melt cools in two stages:

  1. the melt cools at depth slowly enough for phenocrysts to form

  2. the melt erupts, and the remainder cools quickly, so fine-grained groundmass forms around the phenocrysts

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quenching

the sudden cooling to form a solid, transforming the remaining liquid into glass, trapping the earlier-formed crystals within it

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types of "glassy" igneous rocks

obsidian, tachylite, pumice, scoria

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obsidian

-a mass of solid, felsic glass. It tends to be black or brown -extrusive rock; will be around volcanoes

<p>-a mass of solid, felsic glass. It tends to be black or brown -extrusive rock; will be around volcanoes</p>
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pumice

-a felsic volcanic rock that contains abundant (75% to 90% of the rock's volume) tiny vesicles, each surrounded by a thin screen of glass -can look like a sponge -forms from quickly cooling, volatile-rich frothy lava

<p>-a felsic volcanic rock that contains abundant (75% to 90% of the rock&apos;s volume) tiny vesicles, each surrounded by a thin screen of glass -can look like a sponge -forms from quickly cooling, volatile-rich frothy lava</p>
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pyroclastic rock

rock made from fragments that were blown out of a volcano during an explosion and were then packed or welded together

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types of pyroclastic debris

ash and dust, pumice, lapilli, cinders, blocks, bombs

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compositional types of magma/lava and igneous rocks

-felsic (silicic) -intermediate -mafic -ultramafic

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felsic

-65-70% SiO2 -extrusive: rhyolite intrusive: granite -low iron (Fe) and magnesium (Mg) -quartz, k-spar -light-colored

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intermediate

-50-65% SiO2 -extrusive: andesite intrusive: diorite -feldspar (pyroxene or amphibole) -diorite (specified black/white= gray)

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mafic

-45-50% SiO2 -extrusive: basalt -intrusive: gabbro -dark colored -Ca-plagioclase (dark), pyroxene (dark), olivine (dark green)

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ultramafic

  • <45% SiO2 -rich in Fe, Mg -intrusive: peridotite

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igneous rock names

granite, rhyolite, basalt

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granite

-a usually light colored igneous rock that is found in continental crust -felsic -instrusive -has the most silica

<p>-a usually light colored igneous rock that is found in continental crust -felsic -instrusive -has the most silica</p>
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rhyolite

-a light-brown to gray, fine-grained extrusive igneous rock with a felsic composition. -the extrusive equivalent of granite

<p>-a light-brown to gray, fine-grained extrusive igneous rock with a felsic composition. -the extrusive equivalent of granite</p>
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basalt

-a dark, dense, igneous rock with a fine texture, found in oceanic crust -mafic -extrusive

<p>-a dark, dense, igneous rock with a fine texture, found in oceanic crust -mafic -extrusive</p>
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gabbro

-a mafic rock with large grains -intrusive

<p>-a mafic rock with large grains -intrusive</p>
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peridotite

-an ultramafic rock with large grains -intrusive

<p>-an ultramafic rock with large grains -intrusive</p>
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causes of compositional variation

partial melting, fractional crystallization, assimilation

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