Aphanite

[æfәnait]

(noun.) fine-grained homogeneous rock (such as basalt) containing minerals undetectable by the naked eye.

Checked by Anita--From WordNet

(n.) A very compact, dark-colored /ock, consisting of hornblende, or pyroxene, and feldspar, but neither of them in perceptible grains.

Typed by Jed