How could you easily distinguish a black and white gneiss from a similar-colored granite?
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August 4, 2020Mars has an average surface temperature of about 200K
August 4, 2020How could you easily distinguish a black and white gneiss from a similar-colored granite?
Easy-peasy. Look for foliation on the gneiss. Granite is more massive.
A gneiss will have foliation to it (1st pic) – parallel lines that are the result of a pressure/stress regime that forces the minerals to run perpendicular to the stress field. Granites that have not been subjected to a stress field will be massive and no indication of foliation (2nd pic).
This can get tricky when a granite turns into a gneiss – they will look similar but you have to look for the foliation.
