geology exam 2

igneous and sedimentary rocks, volcanoes, and diamonds.

rock

coherent, naturally occurring solid of aggregate minerals

3 rock types

igneous, metamorphic, sedimentary

lava

found on earths surface - extrusive

magma

beneath earths surface - intrusive

what does crystal size tell us?

how fast it cooled

coarse crystal size- phaneritic

slow cooling

medium crystal size - phaneritic

moderate cooling

fine crystal size - aphanitic

fast cooling

coarse and fine - porphyritic

slow then fast

mafic melts

contain a relatively high proportion of magnesium oxide and iron oxide relative to silica

ultramafic melts

even higher proportion of magnesium oxide and iron oxide relative to silica

felsic melts

have a relatively high proportion of silica relative to magnesium and iron oxide

intermediate melts

composition lies partway between those of mafic and felsic melts

where do diamonds form

under extremely high pressures, about 150 km below the surface in cratons

polymorphs of carbon

diamond and graphite

metastable

theoretically unstable, but so long-lived as to be stable for practical purposes - diamond

kimberlite

main host matrix of diamonds

decompression melting

pressure decreases but temperature remains constant, creating a melt. occurs at mantle plumes, continental rifts, and divergent plate boundaries

flux melting

volatiles help break chemical bonds, creating a melt

viscosity

resistance to flow

low viscosity

hotter, mafic, less volatiles

high viscosity

cooler, felsic, more volatiles

columnar jointing

solidified flows may contract with vertical fractures that are hexagonal in cross section - common in basalts

volcanic glass

formed when magma is rapidly cooled

assimilation

magma breaks off rocks, most slowly melt but a few are preserved

geologic settings of volcanism

mid ocean ridges, convergent boundaries, continental rifts, oceanic hot spots, continental hot spots and flood basalts

shield volcano

built up slowly by the accretion of thousands of highly fluid lava flows called basalt

stratovolcanoes

alternate explosive lava eruption with emissions of pyroclastic products, narrow base and steep sides

volcanic domes

formed by relatively small, bulbous masses of lava too viscous to flow any great distance

cinder cones

short eruptions that generally release only pyroclastic product

clastic

loose rock fragments cemented together

biochemical

cemented shells of organisms - nonclastic

organic

carbon-rich remains of once living organisms-nonclastic

chemical

minerals that crystallize directly from water - nonclastic

weathering

natural forces breaking down rocks(in situ) into smaller pieces

erosion

broken pieces are transported or moved from one place to another

deposition

moved particles being deposited in a new location

conglomerate

rounded to partly rounded pebbles, cobbles, or boulders

breccia

angular pebbles, cobbles, or boulders

sandstone

sand grains composed of quartz, feldspar, or other minerals

shale

compacted clay minerals

cross beds

created by ripple and dune migration

graded bedding

the result of sorting during setting, packages of sediment with larger grains at the base and finer at the top

mud cracks

present only in fine-grained rocks with enough clay content to cause shrinking