Gahnite

specimen number:
2063515

location:
Rocky Mtn Boy Claim, Grape Creek, Fremont Co., Colorado, USA

description:
Semi lustrous black opaque octahedral crystals of gahnite to 2.5 cm in size in a cluster with little attached matrix. This is in good condition and quite choice for the species. The specimen comes with a previous label from the collection of Ray DeMark.

Situated southwest of Canon City in Fremont County, Colorado, the Grape Creek district encompasses Proterozoic metamorphic terranes characterized by complex schists, gneisses, and granite pegmatites cut by regional shear zones. Prospectors first explored the area in the late nineteenth century, discovering localized deposits of base and precious metals alongside magnetite iron ore, which led to minor underground mining operations for copper, zinc, gold, and silver into the mid-twentieth century. High-grade metamorphism and regional exhalative processes across zinc-rich precursor sediments formed specialized metamorphic minerals within the country rock and pegmatite dikes. Among these is gahnite, a rare zinc-dominant member of the spinel group, which occurs as distinct, dark green to black octahedral crystals embedded in quartz, feldspar, and mica matrix. Field collectors and mineralogists have targeted the historical mine workings, prospects, and pegmatite outcrops along the Grape Creek drainage to recover sharp gahnite specimens representative of Precambrian metamorphic environments.

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