Rocks Flashcards
(28 cards)
Texture
Texture is very useful for identification of rocks. Texture, or grain, is formed by particles of minerals or other rocks.
Texture is the look and feel of a rock’s surface.
Grain
Grain is particles of minerals or other rocks; basically texture. Grain has a size, a shape, and a pattern.
Coarse grain
Size
Large and easy to see. Can be measured. Example: diorite
Fine grain
Size
Fine grain is so small that it can only be seen clearly with a microscope. Example: slate
No visible grain
Size
Can’t be seen, even with a microscope. Example: flint
Rounded grain
Shape
Mostly uniform grain. Example: conglomerate
Jagged grain
Shape
The grain varies in size. Example: breccia
More on grain shape
Grain can result from the shapes of the crystals that form the rock. It can also result from fragments of several rocks. Example: smooth/ round or jagged
Grains very widely in shape. Some look like sand, small seeds, exploding stars, or more.
Nonbanded
No stripes. Example: Quartzite
Banded
Striped, has visible layers. Example: gneiss
More on grain pattern
Some grains are flat layers like stacked pancakes; others have swirls. Some rocks have grains of different colors in bands; others have randomly occurring grain.
What is the process of breaking down sedimentary rocks, or creating sediment?
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Weathering
By weather (wind, rain, ice), chemical changes, and living things like plants, weathering creates loose material called sediments.
(Sedimentary is the most extensive process in the cycle.)
By which process are sediments moved?
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Erosion
Moving sediments by wind, water (the most powerful), gravity, or ice
The process of depositing sediments?
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Deposition
Sediments stop moving and are deposited in layers.
How is sedimentary rock formed?
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Compaction
The sediments are deeply buried, placing them under pressure due to the weight of the overlying rock layers. The bottom layer is the most immobile and therefore the most compact.
What is the other process of forming sedimentary rock?
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Cementation
New minerals stick the sediment together just like cement. This holds the grains together tightly.
The processes that form metamorphic rock?
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Heat and pressure
Heat
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Caused by magma, which is molten rock beneath earth’s surface. The temperature is hot enough to change the rock‘s structure but not melt it. It is malleable like Play-Doh. Heat can change sedimentary, igneous, or another older metamorphic rock.
Pressure
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Caused by intense collisions and friction of tectonic plates from overlying rock layers. Deep under earth’s surface. Pressure can change sedimentary, igneous, or another older metamorphic rock.
The processes that form igneous rocks?
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Melting, cooling/hardening
Melting
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Caused by increase in temperature in rock deep below earth‘s surface. Also caused by friction between crustal plates. Lava is molten rock material on earth‘s surface; magma is molten rock material under earth’s surface.
Cooling and hardening
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Melted rock turns solid. Slow cooling happens below earth’s surface as magma cools, forming large crystals. Example: granite
Fast cooling happens on the earth’s surface as lava cools, forming small crystals. Example: obsidian, basalt, pumice
More on igneous rocks
(Intrusive vs. extrusive, etc.)
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They are formed when magma or lava hardens. Usually found near volcanoes or fissures. Example: obsidian, granite
They can be fast-cooling. (Extrusive, above the surface, from lava. Usually glassy or has holes from where the gas was trapped.) They can also be slow-cooling. (Intrusive, underground, from magma. Usually has large crystals or many colors.
More on sedimentary rocks
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They are formed when sediments accumulate and compact and cement together. Sediments are often deposited in layers. This type of rock could have sand, pebbles, and often fossils. There may even be boulder-sized particles.
