Publication Date:
2011-05-01
Description:
Cranswickite is a newly recognized mineral of composition MgSO4{middle dot}4H2O from Calingasta, San Juan Province, Argentina (IMA2010-016). Cranswickite is monoclinic, space group C2/c, a = 11.9236(3), b = 5.1736(1), c = 12.1958(3) A, {beta} = 117.548(2){degrees}, V = 667.0(1) A3, Z = 4, dobs = 1.917 g/cm3, and dcalc = 1.918 g/cm3. The mineral occurs0 as a soft white vein filling in a metasedimentary rock. The atomic structure has been determined by direct methods and refined by Rietveld analysis of powder diffraction data. The atomic structure consists of chains of corner-sharing magnesium-containing octahedra and sulfate tetrahedra similar to the structure of pentahydrite. All the water molecules directly coordinate magnesium in the structure. The five strongest lines in the powder X-ray diffraction data are [dobs in angstroms (I) (hkl)]: 5.259 (100) (200), 3.927 (46) (11[IMG]f1.gif" ALT="Formula" BORDER="0"〉), 3.168 (45) (11[IMG]f2.gif" ALT="Formula" BORDER="0"〉), 4.603 (29) (11[IMG]f3.gif" ALT="Formula" BORDER="0"〉), 2.570 (23) (311). Infrared and Raman spectra are very similar to the spectra measured from starkeyite. The chemical composition of cranswickite is the same as starkeyite MgSO4{middle dot}4H2O, but starkeyite has an atomic structure where two sulfate tetrahedra and two Mg(H2O)6 octahedra share corners to form a four-membered ring and not a chain as in cranswickite. The new mineral is named in honor of Lachlan M.D. Cranswick (1968-2010), an Australian crystallographer who helped to developed and maintain the Collaborative Computational Project No. 14 in Powder and Small Molecule Single Crystal Diffraction (CCP14).
Print ISSN:
0003-004X
Electronic ISSN:
1945-3027
Topics:
Geosciences
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