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Webster 1913 Edition

Adj.

(Min.)

Resembling aphanite; having a very fine-grained structure.

aphanitic ‎(comparative more aphanitic, superlative most aphanitic)

(geology) Pertaining to or consisting of aphanites, igneous rocks which have crystals too fine to be seen by the naked eye.

having crystals too fine to be seen by the naked eye