Heulandite with Mordenite

specimen number:
2292140

location:
Rat's Nest Claim, Custer Co., Idaho, USA

description:
Attractive lustrous crystals of heulandite to 2.0 cm in size across the top of a mordenite crystal covered matrix. In great condition.

The Rats Nest claim, located in the Squaw Creek district near Challis, Custer County, Idaho, is a notable mineral locality recognized for top quality heulandite specimens. Geologically, the deposit is situated within the Eocene-aged Challis Volcanic Group, which consists of sequences of dacite and andesite flows, tuffs, and flow breccias. During post-volcanic cooling, hydrothermal fluids migrated through vesicles and structural fractures in the volcanic host rock, depositing silica and zeolites within open cavities. These pockets frequently yielded geode-like nodules containing heulandite crystals perched on top of mordenite. Commercial development and organized surface excavation at the claim began in the late twentieth century, operating predominantly as a specialized specimen-mining venture rather than an industrial metal mine. Mining activity at the site has been carried out intermittently by private claim owners and field collectors, with seasonal extraction of mineral specimens continuing into the twenty-first century.

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