apache tears505a

APACHE TEARS:

"Apache tears" is the popular term for rounded pebbles of obsidian or "obsidianites" composed of black or dark-colored natural volcanic glass, usually of rhyolite composition and bearing conchoidal fracture. Also known by the lithologic term "marekanite", this variety of obsidian occurs as subrounded to subangular bodies up to about 2 inches in diameter, often bearing indented surfaces.[1] Internally the pebbles sometimes contain fine bands or microlites and though in reflected light they appear black and opaque, they may be translucent in transmitted light. Apache tears fall between 5 and 5.5 in hardness on the Mohs scale.Apache tears originate from siliceous lava flows, lava domes or ash-flow tuffs, often in close association with or embedded in, gray perlite. The spherules occur as cores within perlite masses that typically exhibit texture of concentrically curved, onion-skin fractures. Formation is apparently related to differential cooling and various alkali and water contents. Excessive water present during cooling and quenching of rhyolitic lava causes obsidian to hydrate (i.e., water entering the obsidian glass converts it to perlite). Where perlite is incompletely hydrated, fresh obsidian cores remain as pebbles of marekanite or Apache tears.

"The Mineral "Apache Tears"

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