Geology Exam 2

Biomineralization

Biomineralization

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

In the crystalline lattice of minerals,

atoms occur in a specific and repeating pattern

Minerals can form by

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

chemical bonds in minerals

ionic, covalent, metallic, van der waals

chemical bond

the force that holds two atoms or ions together

ionic

-halite, sodium chloride (NaCl) -relatively weak

ionic bond

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

covalent

-diamond, carbon -very strong -shared electrons

covalent bond

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

metallic bond

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

metallic

-native metals -malleable -ductile -sectile

maleable

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

ductile

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

sectile

can be cut with a knife

native metals

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

van der waals

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

properties of a mineral

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

color

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

streak

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

luster

appearance to reflection of light; the way it shines

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

crystal habit

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

cleavage fracture

the way a mineral breaks

glass and porcelain have a

concoidal fracture

chemical groups of minerals

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

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

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

the silicon-oxygen tetrahedra that constitute them are linked

nesosilicates

-isolated tetrahedra -ex: olivine

sorosilicates

-two SiO4 tetrahedra sharing a single oxygen -sister silicates

oxides

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

cations of oxides

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

anion of oxides

oxygen (O^-2)

sulfates

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

carbonates

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

halides

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

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)

native elements (metallic bonds)

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

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

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

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

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.

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

sediment

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

lithification

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

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

cementation

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

magma

melt underground

lava

melt that has emerged to the surface

causes of melting

1. decompression

2. flux melting (addition of volatiles)

3. heat transfer

(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

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

Magma also forms at locations where

volatiles mix with hot mantle rock

volatiles

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

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

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

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

heat transfer melting

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

upward movement causes decompression melting

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

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

intrusive (plutonic) igneous rock

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

aphanitic

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

phaneritic

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

porphyritic texture

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

porphyritic rocks

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

phenocrysts

large crystals in porphyritic rocks

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

quenching

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

types of "glassy" igneous rocks

obsidian, tachylite, pumice, scoria

obsidian

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

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

pyroclastic rock

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

types of pyroclastic debris

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

compositional types of magma/lava and igneous rocks

-felsic (silicic) -intermediate -mafic -ultramafic

felsic

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

intermediate

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

mafic

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

ultramafic

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

igneous rock names

granite, rhyolite, basalt

granite

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

rhyolite

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

basalt

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

gabbro

-a mafic rock with large grains -intrusive

peridotite

-an ultramafic rock with large grains -intrusive

causes of compositional variation

partial melting, fractional crystallization, assimilation

partial melting

the melting in a rock of the minerals with the lowest melting temperatures, while other minerals remain solid

during partial melting,

only part of the source rock melts, so magma tends to be more felsic

fractional crystallization

the process by which a magma becomes progressively more silicic as it cools, because early-formed crystals settle out -the removal and segregation from a melt of mineral precipitates

assimilation

the process of magma contamination in which blocks of wall rock fall into a magma chamber and dissolve

viscosity

A liquid's resistance to flowing

bowen's reaction series

-the sequence in which different silicate minerals crystallize during the progressive cooling of a melt -indicates the succession of crystallization in cooling magma

bowen's reaction series and its relation to partial melting and fractional crystallization

if the liquid separates from the solids at any time in partial melting or fractional crystallization, the chemical composition of the liquid and solid will be different

types of intrusions

dikes, sills, batholiths

tabular intrusions

dikes and sills

dike (discordant)

a tabular (wall-shaped) intrusion of rock that cuts across the layering of country rock -"vertical"/slanted

sill (concordant)

a nearly horizontal tabletop-shaped tabular intrusion that occurs between the layers of country rock -horizontal

batholith

a vast composite, intrusive, igneous rock body up to several hundred km long and 100 km wide, formed by the intrusion of numerous plutons in the same region

plutons

an irregular or blob-shaped intrusion; can range in size from tens of meters across to tens of km across

products of an eruption come in three forms

lava flows, pyroclastic debris, and gas

lava flow

sheets or mounds of lava that flow onto the ground surface or sea floor in molten form and then solidify

pahoehoe

-a lava flow with a surface texture of smooth, glassy, ropelike ridges -hot -lower viscosity -steeper, faster flow