Staurolite

specimen number:
2062256

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

description:
A set of four matrix starlight specimens from this well-known locality. The size provided is the size of the box that these are contained within. Collected in 1997.

Lake Michigamme, located within Marquette County in the Upper Peninsula of Michigan, is a classic American mineral locality renowned for producing sharp, distinct crystals of staurolite, which frequently exhibit pristine ninety-degree cross-shaped penetrative twinning. Geologically, these crystals are hosted within the Paleoproterozoic-age Michigamme Slate, a thick sedimentary sequence of pelitic shales and siltstones that underwent intense regional metamorphism during the Penokean Orogeny. This high-grade metamorphic activity recrystallized the original sedimentary rock into a fine-grained biotite-garnet-staurolite schist, providing the ideal chemical and thermal conditions for large porphyroblasts of dark reddish-brown to black staurolite to slowly grow within the micaceous matrix. Historically, organized quarrying and industrial development at Lake Michigamme dates back to the late nineteenth century, with the opening of several iron ore mines along the Marquette Range, including the Michigamme mine which operated from 1872 through approximately 1905. While commercial mining at the primary iron properties ceased in the early twentieth century, the shoreline exposures, road cuts, and historic waste rock piles near the lake have remained an active destination for targeted manual mineral specimen recovery and geological academic field studies continuously through 2026.

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