aphanitic

noun Petrography.

1. a fine-grained igneous rock having such compact texture that the constituent minerals cannot be detected with the naked eye.

noun

1. any fine-grained rock, such as a basalt, containing minerals that cannot be distinguished with the naked eye

1. Of or relating to an igneous rock in which the crystals are so fine that individual minerals cannot be distinguished with the naked eye. Aphanitic rocks are extrusive rocks that cooled so quickly that crystal growth was inhibited. Compare phaneritic.