File:Staurolite-muscovite schist (Michigamme Formation, Paleoproterozoic; south of the Imperial Mine, near Michigamme, Michigan, USA) (49155783922).jpg
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Staurolite schist from the Precambrian of Michigan, USA. (public display, Seaman Mineral Museum, Michigan Technological University, Houghton, Upper Peninsula of Michigan, USA) Staurolite is a moderately common metamorphic mineral, usually found in schists & gneisses. It is an iron aluminum hydroxy-oxy-silicate mineral, ideally Fe2Al9O6(SiO4)4(O,OH)2. Staurolite is famous for its tendency to form interpenetrating twins - individual crystals tend to cross each other at acute angles, forming "X"s or crosses. These are called cruciform twins. Perfect cross-shaped staurolite twins are sometimes called "fairy crosses" or "fairy stones". Many fairy crosses offered for sale are fakes (carved & dyed rock). Staurolite is nonmetallic in luster, typically dark brown in color, quite hard (H=7 to 7.5), and has no cleavage. Staurolite tends to alter to muscovite mica if potassium (K) is added. The iron of altered staurolite goes into forming hematite. Seen here is a staurolite-muscovite schist from northern Michigan. Schist is a foliated, intermediate- to high-grade, metamorphic rock. This one is from the Michigamme Formation, an ancient succession of metamorphosed marine sedimentary rocks. The unit is heterolithic, with slates, phyllites, schists, meta-iron formations, metaquartzites, metadolostones, metaconglomerates, and some metavolcanic rocks. Stratigraphy: Michigamme Formation, upper Baraga Group, uppermost Marquette Range Supergroup, upper Paleoproterozoic, ~1.85-1.86 Ga (another date in the published literature is 1.93 Ga) Locality: unrecorded/undisclosed site south of the Imperial Mine, west or southwest of the town of Michigamme, Upper Peninsula of Michigan, USA Photo gallery of staurolite: <a href="https://www.mindat.org/gallery.php?min=3753" rel="noreferrer nofollow">www.mindat.org/gallery.php?min=3753</a> |
| Date | |
| Source | Staurolite-muscovite schist (Michigamme Formation, Paleoproterozoic; south of the Imperial Mine, near Michigamme, Michigan, USA) |
| Author | James St. John |
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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/49155783922 (archive). It was reviewed on 2 December 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| current | 06:24, 2 December 2019 | | 3,008 × 2,000 (6.78 MB) | Ser Amantio di Nicolao (talk | contribs) | Transferred from Flickr via #flickr2commons |
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