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With Magma You Get Igneous, Part II

With Magma You Get Igneous, Part II
Reading Level
     edHelper's suggested reading level:   grades 8 to 9
     Flesch-Kincaid grade level:   8.47

Vocabulary
     challenging words:    andesite, batholith, batholiths, biotite, dike, diorite, extrusions, ferromagnesian, hornblende, laccolith, laccoliths, magnesium, olivine, plagioclase, pyroxene, singularly
     content words:    With Magma You Get Igneous Rock, Sierra Nevada Mountain, Black Hills, South Dakota

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With Magma You Get Igneous, Part II
By Trista L. Pollard 		  
1     In With Magma You Get Igneous Rock, Part I, you read about magma and its relationship to igneous rocks. The chemical composition of the magma determines the type of igneous rock that forms. More specifically, it determines the mineral composition of igneous rock. Geologists use this information to divide igneous rock into three different families: felsic, mafic, and intermediate.
 
2     Felsic igneous rock forms when the magma contains a large amount of silica. This type of rock is light in color especially the quartz and potassium feldspar portions of the rock. These rocks also have plagioclase feldspar, biotite, mica, and muscovite mica. The igneous rocks that you will find in this group are granite, pumice, and obsidian.
 
3     Mafic rocks, however, tend to have a dark color. This is due to the lower concentrations of silica in the magma that forms this rock. There is also a high concentration of iron and magnesium. The majority of the minerals that are found in mafic rocks are plagioclase feldspar and pyroxene. Some mafic rocks have ferromagnesian minerals and olivine. Both of these minerals have a dark color. If you happen to find basalt or gabbro, then you have found mafic igneous rock.

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