• journal_title：The Canadian Mineralogist
• Contributor：John M. Hughes ; Forrest E. Cureton ; Joseph Marty ; Robert A. Gault ; Mickey E. Gunter ; Charles F. Campana ; John Rakovan ; André Sommer ; Matthew E. Brueseke
• Publisher：Mineralogical Association of Canada
• Date：2001-
• Format：text/html
• Language：en
• Identifier：10.2113/gscanmin.39.6.1691
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：39
• issue：6
• firstpage：1691
• section：Articles

Dickthomssenite, Mg(V₂O₆)·7H₂O, 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/cm³. 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), 2V_meas 74(1)°, 2V_calc 73°, b = Z, c ∧ Y = 17°. Electron-microprobe analyses yielded (in wt.%) MgO 15.38%, FeO 0.46%, V₂O₅ 73.92%, H₂O (difference) 10.24%, yielding (Mg_0.94Fe_0.02)V₂O₆·1.4H₂O. Dickthomssenite dehydrates rapidly under the electron beam; the crystal-structure determination reveals that there are seven H₂O groups, giving the ideal formula Mg(V₂O₆)·7H₂O. Dickthomssenite is monoclinic, C2/c, a 38.954(2), b 7.2010(4), c 16.3465(9) Å, β 97.602(1)°, V 4544.0(4) ų, Z = 16. The strongest three measured X-ray lines [d in Å(I)(hkl)] are: 9.704(100)(400), 5.843(100)(402), and 3.139(90)(1̅2̅02). The phase is formed of (100) planes of chains of V₂O₆ 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(H₂O)₆ octahedra and non-bonded H₂O molecules. Dickthomssenite is named after Richard W. Thomssen (b. 1933), consulting geologist from Dayton, Nevada, U.S.A.