Types of Rock Quiz Study Guide
Igneous Rocks
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Igneous means fire – all igneous rock is formed from cooled lava or magma
Extrusive rocks – rocks that have formed on the earth’s surface.
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Obsidian, basalt, and pumice are examples of extrusive rocks – very small crystals or no crystals.
“Pits” that have formed as a result of rapidly escaping gases
Intrusive rocks – rocks that have formed inside the earth
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Gabbro, granite, and diorite are examples of intrusive rocks – coarse-grained with larger crystals
(able to see with minimal or no equipment).
Color depends on which minerals were present during formation (pink = feldspar)
Porphyritic Texture – rocks with both large and small crystals.
o Result of two phase cooling: Phase 1 – underground slowly
o Phase 2 – on the earth’s surface (quickly)
Sedimentary Rocks
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Formed from sediments – pieces of other rocks that have broken away due to erosion.
Process:
o Erosion – pieces break away
o Deposition – sediments settle in water
o Compaction – heat and pressure from the earth press the sediments together
o Cementation – minerals dissolved in water fill in spaces between sediments
Clastic Rocks – Form from compressed rock particles
Chemical Rocks – minerals dissolved in a solution crystallize together
Conglomerate is a clastic rock(sediments)
Limetsone is a chemical rock (calcite from shells)
Metamorphic Rock
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“meta” is to change and “morph” is form– metamorphic rock is rock formed from other rocks
due to intense heat and pressure from inside the earth
Metamorphic rocks are categorized as:
o Foliated – grains run in bands that they can split along (like cleavage)
o Non-foliated – grains do not show bands, harder, and do not split
Gneiss (nice) is foliated
Quartzite is non-foliated
Notice that gneiss has strips or bands, while quartzite has no pattern.