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Contents of 6.9 What was the rock before it was metamorphosed?

6.9 What was the rock before it was metamorphosed?

• Metamorphosed igneous rock
• Low to med. grade metamorphism of mafic to intermediate igneous rocks gives dark-colored metamorphic rocks with Fe, Mg micas like chlorite and biotite. If foliated, they are generally schists; if not, they are greenstones.
• Felsic rocks metamorphose to schist if water is present to convert feldspar to muscovite; otherwise, a gneiss may form. Igneous gneisses are less likely to have Al-rich index minerals.