Polished surface of a Staurolite crystal that has been cut across the axis of the twin crossing that is characteristic for this mineral. Staurolite is


Polished surface of a Staurolite crystal that has been cut across the axis of the twin crossing that is characteristic for this mineral. Staurolite is a common metamorphic mineral, a hydrated aluminum silicate mineral that contains iron, magnesium and zinc in variable ratios. Its crystal symmetry is monoclinic, the habitat most often prismatic. Staurolite is famous for its twinned crystals that form into the shape of a cross. Its name comes from the Greek for cross. The twins are the classic penetration type where it appears as if two crystals grew into and out of each other. It actually forms two twin types; one that is nearly 90 degrees and one that is nearly 60 degrees. The 60-degree type is more common but the 90 degree type is the most sought after. It was associated with Christianity as a symbol for the cross and as a good luck charm


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Photo credit: © DIRK WIERSMA/SCIENCE PHOTO LIBRARY / Alamy / Afripics
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Keywords: aluminium, aluminum, axial, axis, christianity, cross, crystal, crystalline, greek, iron, magnesium, metamorphic, mineral, monoclinic, penetration, polished, prismatic, section, silicate, staurolite, surface, twinned, twinning, twins, zinc