Description

#3215 – A 2.9 x 2.4 x 1.4 -inch mineral specimen of clear botryoidal Hyalite Opal nestled on a reddish-brown Rhyolite matrix.  The size of the botryoidal growth of Hyalite Opal is about 1.3 inches across.  The Hyalite Opal fluoresces green under UV light.  This specimen is from Zacatecas, Mexico.  The mineral specimenfrom Zacatecas, Mexico, originates from mid-Tertiary caldera related rhyolitic rocks. 

These rocks are typical of the Sierra Madre Occidental Volcanic Province in the northwestern part of Zacatecas State.  The process of devitrification of these units liberated silica, uranium, iron, and other constituents from the decomposing volcanic glass. The liberated silica, at higher temperatures, tends to precipitate as chalcedony or fine-grained quartz, while at lower temperatures, opal is deposited. The uranium and other elements were redeposited, sometimes as discrete species and in other cases within the framework structure of the chalcedony or opal. Geologic origin provided by New Mexico Tech.  Electric Opal: Green daylight-luminescing hyalite opal from Zacatecas, Mexico.