Orientite

specimen number:
2062280

location:
Manganese Mine, Keweenaw Co., Michigan, USA

description:

Richly crystallized orientite across the top of matrix. Collected in 1995. Very good for the species.

The Manganese mine, situated just south of Manganese Lake near Copper Harbor in Keweenaw County, Michigan, was a small-scale, specialized underground exploration and mining venture focused on extracting manganese oxides rather than the native copper typical of the region. Geologically, the deposit consists of a narrow, steeply dipping hydrothermal fissure vein cutting through the Mesoproterozoic Copper Harbor Conglomerate. Low-temperature, manganese-rich hydrothermal fluids filled these fissures, replacing early calcite and cementing the conglomerate pebbles with dense assemblages of manganite, pyrolusite, and braunite. The vein was first discovered in 1863, leading to the organization of the Buffalo Mining Company, which conducted minor exploration before selling the property. Commercial extraction occurred primarily during a brief period of development between 1881 and 1883 when a shaft was sunk to a depth of roughly 100 feet to extract ore for steel production, but operations were quickly abandoned due to the limited extent of the vein and high transportation costs.

Orientite is a rare calcium manganese silicate mineral that crystallizes in the orthorhombic system, typically forming microscopic, tabular to blocky crystals or prismatic rosettes within mineralized cavities. Geologically, it occurs as a secondary or late-stage hydrothermal mineral in localized manganese-rich volcanic and sedimentary deposits, often resulting from the low-temperature alteration of primary manganese oxides. The mineral displays a resinous to semimetallic luster with a distinct coloration ranging from light reddish-brown to dark chocolate-brown, though it can exhibit brighter orange-brown hues when growing along distinct crystal frameworks. At the Manganese mine locality in Michigan, orientite occurs within small cavities in the basaltic and conglomerate host rocks, typically associated with other complex calcium manganese species like macfallite, along with manganite, calcite, and barite.

Questions about this specimen?
Send an email or call us: 314-341-1811.