: They are often composed of very small crystals of minerals like plagioclase feldspar, augite, or hornblende.
Aphanites are typically (volcanic) rocks. Their signature microscopic structure is the result of rapid cooling: aphanite
: When lava reaches the Earth's surface or shallow subsurface (hypabyssal environments), it cools too quickly for large crystals to grow. : They are often composed of very small
: 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 aphanite
: While the background (matrix) is fine-grained, aphanites frequently contain occasional large crystals called phenocrysts embedded within them.