Spherulite - Lithophysae

Very large and cavernous spherulites are called lithophysae; they are found in obsidians at Lipari, in Yellowstone Park and other places. The characteristic radiate fibrous structure is usually conspicuous, but the fibers are interrupted by cavities that are often arranged as to give the spherulite a resemblance to a rosebud with folded petals separated by arching interspaces. Some of these lithophysae are several centimeters or more in diameter. Tridymite, fayalite and other minerals in the lithophysae may be precipitates from the vapor phase that occupied the cavities. The fibers of these coarse spherulites are alkali feldspar (sanidine or anorthoclase) and tridymite.

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