Describing a fine-grained igneous rock with a glassy or dense appearance, typically composed of feldspar and quartz.
From German 'Felsit,' a combining form from 'Fels' (rock) and '-ite' (mineral suffix). The term emerged in 19th-century mineralogy to describe the texture of certain volcanic rocks that appear uniformly solid rather than crystalline.
Felsitic rocks are like nature's version of frosted glass—their fine crystals are so tiny you can't see individual minerals even with a magnifying glass, but geologists can identify them instantly by how they reflect light.
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