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celsian
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Basalt sample returned by Apollo 15, from near a long sinous lunar valley called Hadley Rille. Measured at 3.3 years old.
(Bed) Rocks and (Flint) Stones
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celsian

mineral
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celsian, an uncommon feldspar mineral, barium aluminosilicate (BaAl2Si2O8), that occurs as hard, light-coloured, glassy masses and crystals in association with manganese deposits in contact zones, as at Jakobsberg, Swed.; Tochigi prefecture, Japan; Rhiw, Wales; near the Omuramba Otjosondjou (dry riverbed), Namibia; and near Incline, Calif., U.S. It may be regarded as the barium equivalent of another feldspar, anorthite, or calcium aluminosilicate (CaAl2Si2O8). Hyalophane is a potassium feldspar containing 5 to 30 percent celsian; it occurs with celsian in contact zones. For detailed physical properties of celsian and hyalophane, see feldspar (table).