Groutite

specimen number:
2062482

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

description:
Excellent example for the species, highly lustrous crystals of groutite averaging 0.4 cm in size in a cluster with minor quartz. In excellent condition.

The Robert Mine was a historical iron and manganese ore producer located on the Cuyuna Iron Range in Crow Wing County, Minnesota, operating primarily during the mid-20th century as part of the region's rich mining district before eventually closing. Geologically, the site is characterized by Paleoproterozoic Biwabik or Cuyuna-style iron-formation strata consisting of folded and weathered sedimentary rock sequences rich in iron and manganese oxides. The mine gained notable mineralogical fame as a classic locality for groutite, a rare jet-black oxide mineral that forms striking, lustrous crystal clusters within the weathered manganese-bearing formations and was originally named in honor of University of Minnesota geology professor Frank F. Grout.

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