brecciated rhyolite associated with gold mineralization - display specimen

Textbook display specimen of breccia in rhyolite from the Monte Cristo Range in Nevada. Initially a light tan, this rhyolite was brecciated by faulting and then hydrothermally altered, with the mineralizing fluids rising through fractures in the breccia and permeating the rhyolite.

This breccia was associated with gold mineralization, and was exposed during development of the Boss Mine, which recovered gold by heap leaching cyanidation. Specimens like these are uncommon and spectacular. 

A breccia, from the Italian for broken, is a rock composed of angular broken fragments that have later been cemented. The fracturing is usually a result of faulting, though there are some mega-breccias  that are the result of the downslope sliding of whole mountain ranges during Cenozoic extension of the Basin and Range province.

The specimen with just a black pencil in the photo is cut flat on one side and is natural on the other. Both sides are shown.

The specimen with pencil and one coin is cut flat on both sides. Both are shown.

Select a specimen: When more than one specimen is shown, you can select a particular specimen by telling us what is in the photo with it, a black and silver pen, a black mechanical pencil, or one of those plus some number of coins, or you can let us make the selection.

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