Pegmatite

A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than 1 cm (0. 4 in) and sometimes greater than 1 meter (3 ft). Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic composition to granite.

However, rarer intermediate composition and mafic pegmatites are known.

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Source: Wikipedia · Image: Wikimedia Commons · CC BY-SA 2.5

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Museum entries, images, and facts are drawn from Wikipedia and Wikimedia Commons, used under public-domain and Creative Commons licenses.