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Hyalite Opal Geode from Mexico

This is a hollow, rhyolitic, geode nodule half containing a botryoidal, bubbly mass of colorless hyalite opal and small quartz flowers, from the Candelaria mine, Moctezuma, Sonora, Mexico. Under short wave UV the hyalite fluoresces bright green, and the hollow geode shell provides an aesthetic setting. The quartz is not fluorescent, but picks up the green light from the emission of the brightly glowing hyalite. The hyalite also fluoresces dim green under long wave UV (not shown). Due to the uranyl-activated mechanism of green fluorescence, this specimen emits a low level of radioactivity, approximately 40 cpm, about twice the natural background level. The size of the geode is 7.6 x 7.5 x 5.8 cm, and it weighs 270 grams.

Fluorescence under short wave UV (254nm)

Interior of geode, photographed under visible light.

Exterior of geode showing rhyolitic shell, photographed under visible light.

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