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Rock Types &

Subtypes

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Three Types of Rocks

• Igneous •Metamorphic •Sedimentary



Igneous Rock • Made from the cooling of magma or lava

• Two categories: – Intrusive – extrusive



Intrusive igneous rock • Made from magma cooling • Magma cools inside of Earth • Magma cools slowly • Slow cooling magma allows large mineral crystals to form

• Intrusive igneous rocks are coarse-grained, which means the grains are big enough to see. You see multiple colors



Intrusive igneous rock Pegmatite


http://geology.com/rocks/pegmatite.shtml


Intrusive igneous rock Granite (Stone Mountain!) – most

common in continental crust


http://geology.com/rocks/granite.shtml


Intrusive igneous rock Gabbro


http://geology.com/rocks/gabbro.shtml


Intrusive igneous rock Diorite


http://geology.com/rocks/diorite.shtml


Intrusive igneous rock Peridotite


http://geology.com/rocks/peridotite.shtml


Extrusive igneous rock • Made from lava cooling • Lava cools outside of Earth • Lava cools quickly • Fast cooling lava does not allow mineral crystals grow very large

• Extrusive igneous rocks are fine-grained, which means the grains very small and hard to see without a microscope. You see one color.



Extrusive igneous rock Andesite


http://geology.com/rocks/andesite.shtml


Extrusive igneous rock Basalt (most common rock

in the oceanic crust)


http://geology.com/rocks/basalt.shtml


Extrusive igneous rock Obsidian – “volcanic glass”


http://geology.com/rocks/obsidian.shtml


Extrusive igneous rock Pumice


http://geology.com/rocks/pumice.shtml


Extrusive igneous rock Rhyolite


http://geology.com/rocks/rhyolite.shtml


Extrusive igneous rock Scoria


http://geology.com/rocks/scoria.shtml


Metamorphic Rock • Metamorphic rocks are formed when preexisting rocks are exposed to extreme heat and pressure

• Metamorphic rocks are found deep within Earth’s crust, so there is a lot of rock on top pressing down.

• Rocks that become metamorphic are so deep in the crust that they are very close to the mantle



Metamorphic Rock • The heat that creates metamorphic rock ONLY comes from the mantle.

• The pressure that creates metamorphic rock ONLY comes from the rock in the upper crust.

• Metamorphic rock is found deep within Earth’s crust.



Metamorphic Rock • There are two types of metamorphic rock: – Foliated – Nonfoliated



Foliated metamorphic rock • Foliated rocks have aligned mineral crystals. The minerals are aligned in planes or bands.

• Sometimes they appear striped or to have squiggles on them.



Foliated Metamorphic Rock Gneiss


http://geology.com/rocks/gneiss.shtml


Foliated Metamorphic Rock Phyllite


http://geology.com/rocks/phyllite.shtml


Foliated Metamorphic Rock Slate


http://geology.com/rocks/slate.shtml


Nonfoliated metamorphic rock

• Nonfoliated rocks have grains that have no obvious organization.

• They are random in their placement.




Amphibolite


http://geology.com/rocks/amphibolite.shtml



Hornfels


http://geology.com/rocks/hornfels.shtml



Marble


http://geology.com/rocks/marble.shtml



Quartzite


http://geology.com/rocks/quartzite.shtml


Sedimentary Rock • Sedimentary rocks are known for their layers, or strata.

• Sedimentary rocks are formed through the processes of: – Weathering – Erosion – Deposition – Compaction – Cementation



Sedimentary Rock • Weathering

– The breaking down of rock due to wind, rain, and temperature change

– Weathering breaks down rocks into small pieces called sediment

• Erosion – The movement of sediment to a new location due to wind, water, ice, or gravity



Sedimentary Rock • Deposition

– The process of sediment being laid down in a new location: typically cracks, crevices, or the bottom of a body of water

• Compaction – As sediments are deposited on top of each other, they are pressed together tightly

• Cementation – Compacted sediments cement together and form rock



Sedimentary Rock • There are three types of sedimentary rocks: – Clastic – Chemical – Organic



Clastic sedimentary rock • Formed when fragments and/or sediments of preexisting rock are compacted or cemented together



Clastic sedimentary rock Breccia



Clastic sedimentary rock Conglomerate



Clastic sedimentary rock Sandstone



Clastic sedimentary rock Shale



Clastic sedimentary rock Siltstone



Chemical sedimentary rock • Chemical rocks are formed when minerals dissolved in water, or another solution, crystallize as the water evaporates



Chemical sedimentary rock Iron Ore



Chemical sedimentary rock Limestone – may form organically as well, called fossiliferous limestone



Chemical sedimentary rock Rock salt – also called by

mineral name, Halite



Organic sedimentary rock • This type of rock is formed from the remains of plants and animals

• If something is organic, it means that at some point, it has been alive. Anything that grows is considered a living thing.



Organic sedimentary rock Coal



Organic sedimentary rock Limestone – also formed chemically.

Fossiliferous limestone is made from bits of coral and other shells


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