aphyric

Aphyric refers to igneous rocks that lack phenocrysts, which are large, conspicuous crystals embedded in a finer-grained groundmass. In simpler terms, an aphyric rock has a uniform texture without noticeably larger crystals. This texture indicates that the magma from which the rock formed cooled relatively quickly, preventing the development of large crystals. Alternatively, the magma might have been too homogeneous or lacked the necessary components for crystal growth.

Aphyric rocks are typically fine-grained or glassy. Their appearance can range from dense and opaque to translucent, depending on the mineral composition and cooling rate. Common examples of aphyric rocks include basalt, rhyolite, and obsidian. The absence of phenocrysts is a key characteristic used in petrology for rock classification. When describing a rock, the term "aphyric" is often used in conjunction with its grain size, such as "aphyric basalt" or "aphyric rhyolite." This designation helps geologists understand the cooling history and potential environment of formation for volcanic and hypabyssal rocks.