Pseudodickthomssenite, Mg(VO3)2·8H2O, a new mineral from the Pickett Corral Mine, Bull Canyon, Montrose County, Colorado, USA

• Published in: Canadian mineralogist Vol. 60; no. 5; pp. 797 - 804
• Main Authors: Kampf, Anthony R, Hughes, John M, Ma, Chi, Marty, Joe
• Format: Journal Article
• Language: English
• Published: Mineralogical Association of Canada 19-09-2022
• Subjects: Bull Canyon; coexisting minerals; Colorado; corvusite; crystal chemistry; crystal structure; dickthomssenite; electron probe data; formula; huemulite; lasalite; Mineralogy; Montrose County Colorado; montroseite; new minerals; nonsilicates; oxidation; oxides; Pickett Corral Mine; pseudodickthomssenite; space groups; trebiskyite; unit cell; United States; vanadates; X-ray diffraction data
• ISSN: 0008-4476; 1499-1276
• DOI: 10.3749/canmin.2200012

Pseudodickthomssenite (IMA2021-027), Mg(VO3)2·8H2O, is a new mineral discovered at the Pickett Corral mine, Bull Canyon, Montrose County, Colorado, USA. The mineral formed from the oxidation of montroseite-corvusite assemblages in a moist environment and occurs on asphaltite and on montroseite-corvusite-bearing sandstone in association with dickthomssenite, gypsum, huemulite, lasalite, and trebiskyite. Pseudodickthomssenite is known only from a diverging cluster of striated needles up to about 500 µm long and 20 µm in diameter; the mineral is light tan in color, with a white streak and a silky luster. The crystals are brittle but somewhat flexible in thin fibers. There are two excellent cleavages, {011} and {011̄}, and the fracture is splintery. The measured density is 1.97(2) g/cm3. Electron probe microanalysis provided the empirical formula [Mg0.99Ca0.01]Σ1.00(V5+O3)2·8H2O. Pseudodickthomssenite is triclinic, P1̄, a=7.3566(6) Å, b=9.4672(9) Å, c=9.5529(9) Å, α=104.205(7)°, β=100.786(7)°, γ=100.157(7)°, V=616.08(10) Å3, and Z=2. The structure of pseudodickthomssenite (R1=0.0307 for 1124 I >2σI reflections) contains V5+O5 polyhedra that link by edge-sharing to form a zig-zag [VO3] chain. MgO2(H2O)4 octahedra link the [VO3] chains into a Mg(H2O)4[VO3]4 sheet and the sheets are linked to one another via a complex network of hydrogen bonding involving Mg(H2O)6 octahedra and isolated H2O groups. The structure is very similar to that of dickthomssenite.