Aphanite

Igneous rock composed of very small crystals invisible to the naked eye

Aphanites are igneous rocks that are so fine-grained that their component mineral crystals are not visible to the naked eye. This geological texture results from rapid cooling in volcanic or hypabyssal environments. As a rule, the texture of these rocks is not the same as that of volcanic glass, with volcanic glass being non-crystalline (amorphous), and having a glass-like appearance.

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