Okieite, Mg3[V10O28]·28H2O, a new decavanadate mineral from the Burro Mine, Slick Rock mining district, San Miguel County, Colorado, USA

• Published in: Canadian mineralogist Vol. 58; no. 1; pp. 125 - 135
• Main Authors: Kampf, Anthony R, Adams, Paul M, Nash, Barbara P, Marty, Joe, Hughes, John M
• Format: Journal Article
• Language: English
• Published: Mineralogical Association of Canada 16-01-2020
• Subjects: Burro Mine; coexisting minerals; Colorado; corvusite; crystal form; crystal structure; dickthomssenite; Hummer Mine; lattice parameters; metal ores; Mineralogy; montroseite; new minerals; nonsilicates; okieite; oxides; San Miguel County Colorado; Slick Rock mining district; space groups; unit cell; United States; uranium ores; vanadates; vanadium ores
• ISSN: 0008-4476; 1499-1276
• DOI: 10.3749/canmin.1900051

Okieite, Mg3[V10O28]·28H2O, is a new decavanadate mineral from the Burro mine, Slick Rock district, San Miguel County, Colorado, USA (type locality); the mineral is also found at the Hummer mine, Paradox Valley, Montrose County, also in Colorado. The mineral is rare; it occurs with dickthomssenite on montroseite- and corvusite-bearing sandstone. Crystals of okieite from the Burro mine are equant to prismatic, commonly appearing like curving columns (up to about 3 mm in length) and often exhibiting rounded faces. The streak of okieite is light orange yellow, and the luster is vitreous. The Mohs hardness is ca. 1 and 1/2, the tenacity is brittle, the fracture is curved or conchoidal, there is no cleavage, and the measured density is 2.20(2) g/cm3. Okieite is biaxial (-), with α=1.720(3), β=1.745(3), γ=1.765(3) (white light); 2V=84(2)° with strong r<v dispersion. The optical orientation is X^a=37°, Y^c=28°, Z^b=31°. No pleochroism is observed in okieite. The empirical formula from electron-probe microanalysis (calculated on the basis of V=10 and O=56 apfu as indicated by the structure) is Mg2.86[H0.28V5+10O28]·28H2O. Okieite is triclinic, P1̄, with a 10.55660(19), b 10.7566(2), c 21.3555(15) Å, α 90.015(6), β 97.795(7), γ 104.337(7)°, and V 2326.30(19) Å3, as determined by single-crystal X-ray diffractometry. The strongest four diffraction lines in the powder diffractograms are [d in Å(I)(hkl)]: 9.71(100) (1̄01, 01̄1, 011, 101); 8.32(19) (1̄10); 11.04(17)(002); and 6.42(12)(110, 1̄1̄1, 11̄2). The atomic arrangement of okieite [R1=0.0352 for 11,327 I>2σI reflections] consists of a {V10O28}6- (decavanadate) structural unit and a {[Mg(H2O)6]3·10H2O}6+ interstitial complex. Only hydrogen bonding links the structural unit with the components of the interstitial complex. Okieite is isostructural with synthetic Mg3[V10O28]·28H2O. The name okieite is for Craig ("Okie") Howell of Naturita, Colorado.