staurolite
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mineral / chemical formula |
properties / significance / occurrence |
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staurolite (Fe,Mg,Zn)2Al9(Si,Al)4O22OH2 |
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Nesosilicate with monoclinic crystals, colored brown to black, pleochroic, mostly opaque (white streak). The mineral is named from the Greek for 'cross' because 35% of its crystals have grown in a classic penetration twinning mode in which it appears as if two crystals grew into and out of each other (at 60º or 90º). Occassionally, paired twins can form star shapes (image). Macroscopically visible crystals are prismatic, and often larger than the surrounding minerals (porphyroblasts), often with poikiloblastic texture on thin-section. Staurolite is an intermediate to high grade regional metamorphic mineral that often occurs associated with other metamorphic minerals, including almandine garnet, micas, and kyanite. |
links: images: crystal 90º, 2, 3, 60º, 2, mixed, 2, 3; rocks: embedded staurolite, embedded crystal surrounded by muscovite, feldspars and small garnets, embedded 60º, staurolite with embedded kyanite; formations: biotite staurolite schist, Barrovian, Highland Boundary Fault, Scotland - staurolite zone; webpages: staurolite, 2, single and double tetrahedron silicates, Fauske, Norway; thin-sections: staurolite quartzite (quartzite), 2, staurolite wp, staurolite, 2, 3, 4, 5, 6, andalusite and staurolite, poikiloblastic porphyroblasts, b, 2, wp, euhedral staurolite (yellow pleochroic) overgrows shear zone between large light coloured plagioclase porphyroblasts, staurolite (St) as relict within poikiloblastic andalusite, staurolite in a muscovite-biotite schist, 2, Metamorphic rocks in thin section; structure: Staurolite (UC), (crystals UC) |
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