Aphanite

Aphanites are typically (volcanic) rocks. Their signature microscopic structure is the result of rapid cooling:

: When lava reaches the Earth's surface or shallow subsurface (hypabyssal environments), it cools too quickly for large crystals to grow. aphanite

is a geological term for igneous rocks with a "fine-grained" texture so compact that individual mineral crystals cannot be seen by the naked eye. Derived from the Greek word aphanḗs , meaning "invisible," these rocks appear as a homogeneous, uniform mass without magnification. Formation and Characteristics Aphanites are typically (volcanic) rocks

: While the background (matrix) is fine-grained, aphanites frequently contain occasional large crystals called phenocrysts embedded within them. Derived from the Greek word aphanḗs , meaning

: They are often composed of very small crystals of minerals like plagioclase feldspar, augite, or hornblende.

: Because they form near the surface, they may contain small holes (vesicles) created by escaping gas bubbles during the cooling process. APHANITE Definition & Meaning - Dictionary.com