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Rhyolite is a high silica fine-grained (aphanitic) igneous rock.
The best way to describe this particular specimen of rhyolite is that
it closely resembles bologna that has turned brown and hardened.
It is also porphyritic; the small clear inclusions are crystals of sanidine feldspar.
Photo is copyright free for
non-commercial educational uses.
Just credit photo to R.Weller/Cochise College.