• journal_title：The Canadian Mineralogist
• Contributor：Anthony R. Kampf ; John M. Hughes ; Joe Marty ; Mickey E. Gunter ; Barbara Nash
• Publisher：Mineralogical Association of Canada
• Date：2011-
• Format：text/html
• Language：en
• Identifier：10.3749/canmin.49.2.595
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：49
• issue：2
• firstpage：595
• section：Articles

Rakovanite, Na₃{H₃[V₁₀O₂₈]}·15H₂O, is a new mineral species from the Sunday and the West Sunday mines, Slick Rock district, San Miguel County, Colorado, USA; the mineral is the natural analog of the previously synthesized phase. Rakovanite is orange, with an orange-yellow streak. Crystals of rakovanite are up to 1 mm in maximum dimension and vary in habit from blocky to prismatic on [100]. The mineral is transparent, with a subadamantine luster; it does not fluoresce in long- or short-wave ultraviolet radiation. Rakovanite displays brittle tenacity, and has a Mohs hardness of 1. No cleavage or parting was observed, and the mineral displays a conchoidal fracture. The density calculated from the ideal formula and the single-crystal cell data is 2.407 g cm⁻³. Rakovanite is biaxial (+), with α_589nm = 1.776(5), β_589nm = 1.803(5), γ_589nm = 1.910(6). The measured values of 2m>Vm> are: 2m>Vzm>_540nm = 58(1); 2m>Vzm>_589nm = 56(1); 2m>Vzm>_650nm = 53(1)°. Dispersion is m>rm> < m>vm>, strong, parallel; orientation: m>Xm> = b; m>Zm> /\ c = 8m>°m> in obtuse β. The pleochroic scheme in rakovanite is: m>Xm> light yellow, m>Ym> orangish yellow, m>Zm> yellowish orange, m>Zm> > m>Ym> > m>Xm>. Its chemical composition was obtained by electron-probe microanalysis and the crystal-structure refinement; the empirical formula (V = 10 m>apfum>) is (Na_2.90K_0.07Ca_0.01Al_0.01)_∑2.99{H_2.98[V₁₀O₂₈]}·15H₂O, and the simplified formula is Na₃{H₃[V₁₀O₂₈]}·15H₂O. Rakovanite is monoclinic, space group m>Pm>2₁/m>nm>, with m>am> 12.0248(17), m>bm> 17.121(3), m>cm> 18.140(3) Å, β 106.242(8)°, and m>Zm> = 4; the strongest four lines in the powder-diffraction pattern [m>dm> in Å(I)(m>hklm>)] are: 11.270(100)(1̅01), 7.696(81)(021), 8.709(78)(002), and 6.892(63)(120). The atomic arrangement of rakovanite has been refined to m>Rm>₁ = 0.0383; the structural unit in the phase is formed of a triply-protonated decavanadate polyanion, {H₃[V₁₀O₂₈]}. The structural units are linked by the interstitial complexes, the (Na₃·15H₂O) contents of which balance the +3 charges of the decavanadate polyanion with a NaO₄(H₂O)₂ group, a Na₂(H₂O)₁₀ dimer, and three H₂O molecules that do not bond to the interstitial cations.