When teaching about igneous rocks, one trick instructors often implement to help students determine the igneous composition of the samples is to use the color of the rocks as a guide
Explain how the color of an igneous rock can often be used as an indicator of its igneous composition. Be sure to reference specific minerals for each composition.
What will be an ideal response?
Answer: Generally speaking, mafic rocks contain ferromagnesian minerals like pyroxene and amphibole and are therefore very dark because of the high iron and magnesium content. Felsic rocks, which contain light-colored silicate minerals such as quartz and potassium feldspar, are very light in color. Intermediate rocks, which are a combination of mafic and felsic materials, are somewhere between mafic and felsic on the color spectrum. Common intermediate minerals include plagioclase feldspar, amphibole, pyroxene, and biotite mica.
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What will be an ideal response?
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