Spherulite - Occurrence

Occurrence

Spherulites are most common in silica-rich glassy rocks. Sometimes they compose the whole mass; more usually they are surrounded by a glassy or felsitic base. When obsidians are devitrified, the spherulites are often traceable, though they may be more or less completely recrystallized or silicified. In the center of a spherulite there may be a crystal (e.g. quartz or feldspar) or sometimes a cavity. Occasionally spherulites have zones of different colors, and while most frequently spherical, they may also be polygonal or irregular in outline. In some New Zealand rhyolites the spherulites send branching cervicorn processes (like stags horns) outwards through the surrounding glass of the rock. The name axiolites is given to long, elliptical or band-like spherulites.

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