aphanitic

/ˌæfəˈnɪtɪk/
adjective
  1. Describing an igneous rock whose individual mineral crystals are too small to be seen with the naked eye.
    • The aphanitic texture of basalt makes it look smooth and featureless to the untrained eye.
    • Geologists use a microscope to identify the minerals in aphanitic rocks like rhyolite.
    • Unlike granite, which has visible crystals, aphanitic lava flows cool so quickly that crystals cannot grow large.
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