Straczekite, a New Calcium Barium Potassium Vanadate Mineral from Wilson Springs, Arkansas

Howard T. Evans Jr., Gordon Nord, John Marinenko and Charles Milton
US Geological Survey, Reston, Virginia 22092, USA
George Washington University, Washington DC 20006, USA

Abstract: Straczekite, a new calcium barium potassium vanadate from Wilson Springs (formerly Potash Sulfur Springs), Arkansas, occurs as a rare secondary mineral in fibrous seams in gangue. The dark greenish-black crystals are very soft, thin laths up to 0.5 mm in length, forming thick masses. No single-crystal X-ray patterns could be obtained, but good electron diffraction patterns yielded a monoclinic unit cell in space group C2/m, C2, or Cm. The cell parameters were refined by least squares analysis of Guinier-Hägg X-ray powder data: a 11.679(2), b 3.6608(4), c 10.636(2)Å, β = 100.53(4)° (strongest lines are: 003, 3.486, 100; 001, 10.449, 50; 020 1.8306, 50; 6¯01/510, 1.9437, 15; 111/2¯03, 3.255, 10; 311/3¯12, 2.492, 10; 021, 1.8030, 10). Chemical analysis yields the formula: (Ca0.39Ba0.31K0.33Na0.11)(V1.594+V6.315+Fe0.103+)O20.02(H2O)2.9. The calculated density is 3.21 g/cm3. The mineral conforms to a series of synthetic vanadium bronzes, typified by Ag1-xV2O5 of known structure. It represents a new series of layer vanadate minerals of general formula MxV8O20·yH2O, similar in properties but distinct from the hewettite series (MxV6O16·yH2O).

Mineralogical Magazine; June 1984 v. 48; no. 347; p. 289-293; DOI: 10.1180/minmag.1984.048.347.16
© 1984, The Mineralogical Society
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