Cryptomelane

specimen number:
1392119

location:
Montreal mine, Iron Co., Wisconsin, USA

description:

This is a wonderful large example for the species. Black botryoidal cryptomelane is covering the top of this matrix. This is in super condition. As good as it can get for the species from this old locality. The specimen identification was confirmed at the A. E. Seaman Museum in Michigan. The specimen was on public display at the Tucson, 1997 show, as well as the East Coast, 2018 show.

Cryptomelane from the Montreal Mine in Iron County, Wisconsin occurs in the oxidized zones of the Gogebic Range iron deposits, a major iron mining district active from the late 19th century into the 20th century. The Montreal Mine worked banded iron formation for hematite and magnetite ore, and secondary manganese oxides such as cryptomelane formed in fractures and cavities during weathering. Cryptomelane is a potassium manganese oxide mineral typically appearing as black botryoidal or fibrous crusts associated with other manganese oxides and iron minerals. Specimens from the Montreal Mine are of interest to collectors because they represent uncommon secondary mineralization within a classic Lake Superior region iron mining locality.

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