Rhyolite (quartz porphyry) from Saaremaa, Estonia.

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Rhyolite exposed at the bottom of the Baltic Sea. It is more often referred to as a "red quartz porphyry of the Baltic Sea". This rock is very old, from the Proterozoic. The pebble was found on the coast. It is a fragment of glacial debris. The gray spots are quartz phenocrysts in a fine-grained matrix of mostly K-feldspar and quartz. The width of the image is 9 cm.

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Size: 4272px × 2848px
Location: Saaremaa, Estonia.
Photo credit: © Siim Sepp / Alamy / Afripics
License: Royalty Free
Model Released: No

Keywords: phenocryst, porphyry, proterozoic, quartz, rhyolite