Colemanite after Inyoite

specimen number:
2063258

location:
Corkscrew Mine, Inyo Co., California, USA

description:
What was once a tabular crystal of inyoite, this now replaced by sparkling micro crystals of colemanite. In great condition. The specimen comes with a previous label from the collection of Ray DeMark, who acquired the piece during a trip to Boron, California in 1975 from Vince Morgan.

The Corkscrew Mine in Inyo County, California, USA, is a historic borate deposit located within the Death Valley region. Geologically, the site consists of Tertiary lacustrine sedimentary rocks enriched with hydrous calcium borates, formed through hydrothermal activity and evaporation in ancient lake basins. Mining operations in the area primarily extracted valuable borate minerals like colemanite during the early to mid 20th century. For mineral collectors, the mine is particularly famous for producing superb pseudomorphs of colemanite replacing earlier formed inyoite crystals. In these pseudomorphs, the original blocky monoclinic crystal habit of inyoite is preserved, while the chemical composition and internal structure have been completely replaced by crystalline colemanite, offering a fascinating glimpse into the secondary alteration processes of borate mineralogy.

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