The Scheme for Igneous Rock Identification

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The Scheme for Igneous Rock Identification
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A Brief Tour
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Crystal size
Grain Size
Description
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Intergrown
5
Intergrown
6
Intergrown
7
Not Intergrown
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Where it was formed
Outside the volcano Extrusive
Inside the Earth Intrusive
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Bubbles?
Yes Vesicular
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Bubbles?
NoNon-vesicular
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Color
Neither Light nor Dark
Very Light
Not Very Dark
Not Very Light
Very Dark
Light
Dark
Darkest
Lightest
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Density
Light
Dense
Medium Density
Very Light
Very Dense
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Finding The Minerals
Unless you have other information, work in the
middle of the rocks box.
Identify the rock.
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This is the amount of Potassium Feldspar in the
rock.
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This is the amount of Quartz in the rock.
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This is the amount of Plagioclase Feldspar in the
rock.
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Use tick marks on a scrap paper to measure the
percentage.
Potassium Feldspar 25
Quartz 40
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Practice
Name a light-colored, fine-grained rock with no
bubbles.
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Name a coarse-grained, dense rock.
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Name a very light-colored, glassy, extrusive
rock with bubbles.