Orientite
specimen number:
2062241
location:
Manganese Mine, Keweenaw Co., Michigan, USA
description: The Manganese mine, situated just south of Copper Harbor in Grant Township within Keweenaw County, Michigan, was a small, historically unique mining and exploration venture located near the northern tip of the Keweenaw Peninsula. Geologically, this deposit differs significantly from the native copper systems characteristic of the region, consisting instead of a narrow, hydrothermally mineralized fissure vein cutting through the Mesoproterozoic Copper Harbor Conglomerate. Low-temperature hydrothermal fluids migrating through regional fault lines deposited concentrated manganese and iron carbonates and oxides, filling open fissures and replacing calcite within the host sedimentary and basaltic rocks. Historically, the deposit was first noted in the late 1830s during regional surveys by Michigan state geologist Douglass Houghton, but active development did not begin until 1881 when the Cambria Iron Company excavated a 75-foot-deep open cut to extract approximately 800 tons of material. In 1883, a formal shaft was sunk to remove an additional 400 tons of ore for processing, but metallurgical testing revealed that the high-silica manganese ore was unsuitable for commercial steel manufacturing, leading to the permanent abandonment of all operations later that year. Through 2026, while the historic workings are completely overgrown and inactive, the site remains internationally famous among mineralogists as the type locality for orientite, a rare complex calcium manganese silicate mineral officially discovered and described from the old mine dumps in 1921 that occurs as minute, dark brown prismatic crystals and radiating aggregates.
Micro crystals of orientite in pockets throughout this matrix. Good example for the species. Collected in 1996.
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