Granodiorite differs from diorite by the presence of quartz, and the predominance of plagioclase over alkali feldspar distinguishes it from granite. Although it isn't true granite, granodiorite is one of the granitoid rocks. Rusty colors reflect weathering of rare grains of pyrite, which releases iron. The random orientation of grains shows that this is a plutonic rock. This specimen is from southeastern New Hampshire.
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