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Describe textures of igneous rocks:
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Physical Geo MidTerm
Physical Geology Midterm Terms
| Question | Answer |
|---|---|
| Describe textures of igneous rocks: | Igneous rocks are aphanitic if they're fine-grained, phaneritic if they're coarse-grained |
| What is a batholith | light-colored granite, an intrusive, coarse-grained, nonvolcanic rock |
| A rock has a medium gray, fine-grained groundmass with large crystals of plagioclase, would you expect to see glassy texture? | No |
| What is porphyritic texture? | Small and large crystals in one rock, usually formed from two stage cooling of a melt |
| Describe granite | is a phaneritic rock. is felsic in composition logically could be found in a batholith. is the coarse-grained equivalent of rhyolite. |
| Give examples of glassy textured rocks | obsidian |
| After an explosive volcanic eruption on an island, the surrounding sea is full of light gray floating rock. What must it be? | Pumice |
| Describe scoria | medium to dark gray in color, it's rich in heavy component atoms like iron, and although it is vesicular, it doesn't have enough vesicles (air spaces) to be less dense than water. |
| What are some settings for igneous activity? | hotspots, continental rifts, volcanic arcs bordering ocean trenches, mid-ocean ridges |
| Describe volcanic arcs | form where subduction takes place, are long, curving mountain chains adjacent to deep-ocean trenches, can be continental or island, occur at convergent plate boundaries. |
| Solid blocks of country rock (or wall rock) may... | be broken off by intruding magma, melt entirely and thus change the chemical composition of the intruding magma, not melt but instead remain as recognizable blocks called xenoliths. |
| Volatiles that come out of the Earth as volcanic products may... | may comprise roughly 15% of the magma present, usually consist of 50% water vapor, include H2O, CO2, N, H, and SO2, contribute to Earth's atmosphere and oceans, were dissolved in the molten rock and released as the surrounding pressure lessene |
| Intrusive igneous rocks | cool slowly and are coarse grained |
| Bowen's reaction series shows the | has a discontinuous track in which each step yields a different class of SiO4 mineral, has a continuous track in which there's a progressive change from Ca rich to Na-rich plagioclase |
| Bowen's reaction series shows the | sequence in which different SiO4 minerals form during the progressive cooling of a mafic melt |
| Sedimentary rocks can form | by the precipitation of minerals from water solution, by the cementing together of loose grains of preexisting rock, from shell fragments or carbon-rich relicts of plants. |
| What is the correct listing from smallest to largest of clasts | mud (clay,) silt, sand, pebbles, cobbles, boulders |
| Why would you find the most chemical weathering in a tropical rainforest? | Heat, moisture, and increased surface area are the three factors that speed the rate of chemical weathering |
| Methods of physical weathering of rock include | frost wedging, jointing, salt wedging, thermal weathering, root wedging |
| spalling | rock breaking off in sheets due to thermal expansion, then contraction |
| detritus | Pieces of broken rock produced by physical weathering |
| saprolite | is rotten rock produced in warm, wet regions |
| hydration | absorption of water into crystal structure and its subsequent expansion |
| breccia | nonmarine clastic sedimentary rock composed of angular fragments surrounded by matrix |
| travertine (chemical limestone) | is crystalline calcium carbonate that has precipitated out of groundwater. |
| If you find graywacke in the place where it formed, you know you are looking at an ancient: | avalanche on a submarine slope |
| Graywacke | informal term used for sedimentary rock consisting of sandsize p to small pebble size grains of quartz and rock fragments all mixed together in a muddy matrix, typically occurs at the base of a graded bed |
| shale | A clastic sedimentary rock with clay and silt-sized grains that breaks in thin sheets is called |
| Both chert and limestone may have either chemical or biochemical origin, true or false | True |
| Are gypsum and halite carbonate or evaporite minerals? | Evaporite |
| Are chemical sedimentary rocks crystalline or folioted in texture? | Crystalline |
| List methamorphic rocks in increasing degrees of metamorphism | shale, slate, phylite, schist,gneiss |
| What is a protolith | parent rock |
| metasomatism | process by which hydrothermal fluids change the chemical composition of a rock |
| shield | older portion of the continent that has been exposed by erosion, oldest areas of Earth's surface |
| Shock metamorphism | effects of shock-wave related deformation and heating during impact events |
| Pick out the rock that is nonfoliated: hornfels, phyllite, slate, schist, gneiss | hornfels |
| Retrograde metamorphism | involves the reconstitution of a rock via revolatisation under decreasing temperatures and usually pressures |
| prograde metamorphism | change of mineral assemblages with increasing temperature and pressure conditions |
| blueschist metamorphic rock | rock that forms by the metamorphism of basalt and rocks with similar composition at high pressures and low temperatures |
| pluton | body of intrusive igneous rock that crystallized from magma slowly cooling below the surface of the Earth (think blob of cooling magma) |
| Where does the blue color in a blueschist come from? | glaucophane, a blue mineral |
| List some types of plutons | batholiths, dikes, sills, laccoliths, lopoliths |
| What are some minerals that are only found in metamorphic rocks? | Stuaruolite, kyanite, sillimanite, garnets |
| What is foliation? | planar arrangement of minerals due to metamorphism |
| What is the size of a boulder in mm? | 256 mm |
| What is the size of a cobble? | Between 66 and 256 mm |
| What is the size of a pebble? | between 2mm and 64mm |
| What is the size of sand grain? | 1/16mm and and 2 mm |
| What is the size of silt? | 1/256mm and 1/16mm |
| What is the size of mud(clay)? | Less than 1/256 mm |
| neocrystallization | new minerals formed with changes in pressure and temperature in metamorphic processes |
| What is chemical weathering? | chemical reactions that alter or destroy minerals when rocks come in contact with water solutions or air |
| What are some types of chemical weathering? | Hydrolysis, oxidation, hydration |
| True or false, during chemical weathering, rocks break down into smaller pieces | False |
| True or false, changes in pressure, volatile content and temperature trigger melting in the lower mantle and outer core. | False, these changes trigger melting in the upper mantle and lower crust. |
| What elements make up lava in varying proportions? | Silicon, oxygen, iron, magnesium, calcium |
| Does the composition of magma depend on its source or is it a fairly constant composition? | The composition of magma depends on its source. |
| viscosity | resistance to flow |
| What does viscosity depend on? | composition, temperature, and gas content |
| dike | tabular intrusions that cut vertically across rock that does not have layering |
| xenolith | stopped block that does not melt entirely but becomes surrounded by new igneous rock |
| True or false, all magmas erupt | false |
| true or false, magma freezes (cools from liquid to solid)when exposed to cooler environments | true |
| What are the factors that determine the type of magma | source rock composition, partial melting, assimilation, magma mixing, fractional crystallization |
| What influences how fast magma cools? | Depth of intrusion, shape and size of magma body, presence of circulating groundwater |
| What are the varieties of igneous rock textures? | Crystalline (aphanitic and phaneritic), glassy, and fragmental (pyroclastic) |
| True or false, basalt and gabbro have different compositions, they just form in the same places | False, basalt and gabbro have the same chemical composition, they just cool at different rates |
| True or false, magma tends to be more mafic than the rock from which it was extracted | False, magma is usually more felsic than the rock from which it is extracted |
| What are some mechanisms/factors in chemical weathering? | Dissolution, hydrolysis, oxidation, hydration, relative stability minerals, and chemical weathering produced by organisms. |
| Does weathering occur closer to the surface or deeper in the surface? | Closer to the surface |
| Are sedimentary rocks classified on composition and grain size or cooling rate? | Composition and grain size |
| True or false, limestone consists of calcite shells or shell fragments | True |
| Some sedimentary rocks consist of plant debris that were baked by heat | False, plant debris are buried and altered |
| bed | a single layer of sediment or sedimentary rock with a recognizable top and bottom |
| strata | the several sedimentary beds together |
| bedding plane | the boundary between two sedimentary beds |
| True or false, dolomite and chert form by reaction of preexisting rock with groundwater | True |
| stratigraphic formation | sequence of strata distinctive enough to be traced across a fairly large region |
| ripples | relatively small, elongated ridges that form on a bed surface at right angles to the direction of current flow |
| dunes | larger versions of ridges, usually moved by ocean waves or wind |
| turbidity currents | submarine suspension of sediment |
| turbidite | a sequence of strata deposited by turbidity currents |
| True or false, sedimentation occurs in discrete episodes | true |
| What are the main terrestrial sedimentary environments? | glacial, mountain-stream, alluvial-fan,sand dunes, lake, river |
| What are the main marine sedimentary environments? | delta, coastal beach, shallow-marine clastic, shallow-water carbonate, deep marine |
| Can we determine depositional environments by examining rock types and sedimentary structures? | Yes |
| diagenesis | all of the physical, chemical, and biological processes that transform sediment into sedimentary rock and alter characteristics of sedimentary rock once the rock has formed |
| lithification | the process by which loose sediments turn into rock |
| What are some of the possible products of chemical weathering? | Clays and ions in solution |
| transgressions | when sea level rises and coastlines migrate inward into the continent |
| regressions | when sea level falls and the coastline migrates towards the sea |
| Give example of vesicular rocks | scoria, pumice |
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