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Spherulites in the Hot Creek rhyolite flow, Long Valley Caldera

By California Volcano Observatory
A hand holds a geologic scalebar against the face of an outcrop. The outcrop is a mix of large, pink, circular crystal masses interspersed with black glassy chunks, both several cm in diameter.
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Detailed Description

Spherulites are distinctive rounded masses of radiating needle-like crystals which form by devitrification, a process where glassy, non-crystalline substances restructure into crystalline ones. USGS photo by Jessica Ball.

Sources/Usage

Public Domain.