aphanite

Noun. (geology) Certain dark igneous rocks having grain so fine that the individual crystals cannot be seen with the naked eye.

This is an unmodified, but possibly outdated, definition from Wiktionary and used here under the Creative Commons license. Wiktionary is a great resource. If you like it too, please donate to Wikimedia.

This entry was last updated on RefTopia from its source on 3/20/2012.