Chamosite after Almandine

specimen number:
8311428

location:
Spurr Mine, Marquette Co., Michigan, USA

description:
Classic pseudomorph specimen for this area, crystals of what were once almandine to 2.3 cm in size on matrix and replaced by chamosite. In great condition.

The Spurr Mine, located in the Michigamme area of the Marquette Iron Range in Baraga County, Michigan, is situated within the Paleoproterozoic-aged Marquette Range Supergroup. Geologically, the site is famous for its large almandine garnets that have been completely or partially replaced by chamosite, an iron-rich member of the chlorite group, through retrograde metamorphism or hydrothermal alteration. These pseudomorphs often retain the sharp dodecahedral or trapezohedral crystal forms of the original garnets while exhibiting the dark green, earthy luster characteristic of chamosite. Historically, the Spurr Mine opened in 1872 as an iron ore quarry and underground operation focusing on high-grade magnetite hosted within the Bijiki Iron Formation. The mine operated sporadically over the following decades, with significant activity occurring between 1873 and 1883, and again in the early 20th century before closing permanently around 1913. As of 2026, the historical mine dumps remain a significant destination for mineralogists studying metamorphic processes and the unique iron-silicate chemistry of the Lake Superior region.

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