Chamosite after Almandine

specimen number:
2062203

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

description:
Classic Michigan pseudomorph specimen was sharp crystals of what were once almandine to 2.8 cm in size, these now replaced by dark green to black chamosite. Set nicely on matrix and in great condition.

The Michigamme Mine, located on the western end of the Marquette Iron Range in Michigan, was a notable producer of hard magnetite and hematite ore. Geologically, the deposit is hosted within the Paleoproterozoic Negaunee Iron Formation, where the ore bodies were concentrated through structural folding and metamorphic processes associated with the Penokean Orogeny. This locality is world-famous among mineralogists for its remarkable pseudomorphs of chamosite after almandine garnet, where large, well-formed dodecahedral garnet crystals were chemically replaced by dark green, fine-grained chlorite while perfectly retaining their original crystal shape. Historically, the Michigamme Mining Company began development of the site in 1872, with the mine operating as a significant underground facility through the late 19th century. Production was most consistent between 1872 and 1905, though some intermittent activity occurred until the mid-20th century. Today, the mine is closed and the site is largely reclaimed, but the surrounding waste piles remain a legendary destination for collectors seeking these iconic green pseudomorphs and other metamorphic minerals characteristic of the Michigan iron districts.

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