Groutite

specimen number:
2133071

location:
Robert Mine, Crow Wing Co., Minnesota, USA

description:
Lustrous black crystals of groutite across the front of this matrix. In good condition. Good example for the species.

The Robert Mine in Crow Wing County, Minnesota, is a small historic iron mining locality in the Cuyuna Range, an area known for iron rich deposits in Precambrian rocks. Mining in the region took place mainly during the early to mid 20th century and focused on iron ore. The locality is also known to mineral collectors for groutite, a manganese oxide hydroxide mineral that occurs as dark brown to black prismatic crystals and fibrous aggregates. Groutite from the Robert Mine is of interest due to its crystal form and association with other manganese minerals in the oxidized zones of the deposit.

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