Chamosite after Almandine

specimen number:
2062019

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

description:
A large loose crystal of what was once almandine, this now in the process of being replaced by chamosite. Classic pseudomorph for this area. In great condition, the specimen was collected around the year 1950.

A pseudomorph is a mineral specimen in which one mineral replaces another while preserving the original crystals external shape. In the case of chamosite after almandine, the original almandine garnet crystal was chemically altered and replaced by chamosite, a chlorite group mineral. The resulting specimen keeps the typical garnet crystal form even though the internal composition has changed. Such specimens are valued because they clearly show the process of mineral replacement while preserving the earlier crystal shape.

The Michigamme Mine in Marquette County, Michigan was part of the Marquette Iron Range in the Upper Peninsula, one of the earliest iron mining regions in the United States. Mining developed in the late 19th century to extract iron ore from Precambrian banded iron formation. Underground workings supplied hematite ore for the growing iron and steel industry around the Great Lakes. Like many mines in the district, production eventually declined as higher grade deposits were exhausted and mining shifted to other areas.

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