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DICKTHOMSSENITE, Mg(V2O6){middle dot}7H2O, A NEW MINERAL SPECIES FROM THE FIREFLY PIGMAY MINE, UTAH: DESCRIPTIVE MINERALOGY AND ARRANGEMENT OF ATOMS

2001; Mineralogical Association of Canada; Volume: 39; Issue: 6 Linguagem: Inglês

10.2113/gscanmin.39.6.1691

1499-1276

John M. Hughes, F. Cureton, J. Marty, R. A. Gault, M. E. Gunter, Charles F. Campana, John Rakovan, A. J. Sommer, Matthew E. Brueseke,

Crystal Structures and Properties

Dickthomssenite, Mg(V 2 O 6 )·7H 2 O, is a new mineral species from the Firefly–Pigmay uranium–vanadium mine, San Juan County, Utah. The phase crystallizes as platy light golden brown crystals up to 1.5 mm in length, with white streak and vitreous luster. Its Mohs hardness is 2½, its calculated density, 2.037(1), and its observed density, between 1.96 and 2.09 g/cm 3 . Dickthomssenite displays a perfect {100} cleavage. In 589.3 nm light, the mineral is translucent, α 1.6124(3), β 1.6740, and γ 1.7104(4), 2 V meas 74(1)°, 2 V calc 73°, b = Z, c ∧ Y = 17°. Electron-microprobe analyses yielded (in wt.%) MgO 15.38%, FeO 0.46%, V 2 O 5 73.92%, H 2 O (difference) 10.24%, yielding (Mg 0.94 Fe 0.02 )V 2 O 6 ·1.4H 2 O. Dickthomssenite dehydrates rapidly under the electron beam; the crystal-structure determination reveals that there are seven H 2 O groups, giving the ideal formula Mg(V 2 O 6 )·7H 2 O. Dickthomssenite is monoclinic, C 2/ c , a 38.954(2), b 7.2010(4), c 16.3465(9) A, β 97.602(1)°, V 4544.0(4) A 3 , Z = 16. The strongest three measured X-ray lines [ d in A(I)( hkl )] are: 9.704(100)(400), 5.843(100)(402), and 3.139(90)(1202). The phase is formed of (100) planes of chains of V 2 O 6 divanadate edge-sharing polyhedra containing [2 + 3]-coordinated vanadium atoms, linked in (100) by corner-sharing with Mg octahedra. These (100) planes are linked along [100] by layers of Mg(H 2 O) 6 octahedra and non-bonded H 2 O molecules. Dickthomssenite is named after Richard W. Thomssen (b. 1933), consulting geologist from Dayton, Nevada, U.S.A.