Spherulite - Megaspherulites


Occasionally spherulites are found that are many centimeters and, even more rarely, up to two or three meters in diameter. Those spherulites, which are more than 20 centimeters in diameter, are called megaspherulites. Near Silver Cliff, Colorado, megaspherulites, which range in diameter from 0.30 to 4.3 meters occur within a thick layer of rhyolitic vitrophyre. Megaspherulites as large as 0.91 meter occur within rhyolite exposures on Steens Mountain, Oregon and ones as large as 1.83 meters in diameter occur within welded tuffs exposed near Klondyke, Arizona. The best known occurrence of megaspherulites are stone balls, which range in diameter from 0.61 to 3.35 meters, found around Cerro Piedras Bola in the Sierra de Ameca between Ahualulco de Mercado and Ameca, Jalisco. As often happens with considerably smaller spherulites, these megaspherulites have been released by weathering from an ash flow tuff, in which they originally formed, to create natural stone balls.

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