• journal_title：American Mineralogist
• Contributor：Anthony R. Kampf ; Barbara P. Nash ; Thomas A. Loomis
• Publisher：Mineralogical Society of America
• Date：2013-02-01
• Format：text/html
• Language：en
• Identifier：10.2138/am.2013.4322
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：98
• issue：2-3
• firstpage：439
• section：Article

Phosphovanadylite-Ca, Ca[V⁴⁺₄P₂O₈(OH)₈]•12H₂O, is a new mineral from the South Rasmussen (or South Rasmussen Ridge) phosphate mine, Soda Springs, Caribou County, Idaho. It is named as the Ca analog of phosphovanadylite, which is now renamed as phosphovanadylite-Ba. The new mineral grows on matrix containing fine-grained quartz, massive, porous fluorapatite and hydroxylapatite, framboidal pyrite, and tiny, euhedral sphalerite crystals. Other minerals directly associated with the new mineral are sincosite and native Se. Phosphovanadylite-Ca crystallized at ambient temperatures from late-stage aqueous solutions of near neutral pH under relatively reducing conditions. The mineral is cubic, space group [IEQ]m>Im>43m>mm>, m>am> = 15.441(11) Å, m>Vm> = 3682(5) ų, and m>Zm> = 6. Crystals occur as small, greenish-blue simple cubes (to 0.1 mm on edge) intergrown to form thin crusts. Penetration twinning on {111} is common. The color is bright greenish blue, the streak is very pale greenish blue, and the luster is vitreous. The Mohs hardness is estimated at 2. The new mineral is brittle with irregular fracture and no cleavage. The measured density is 2.02(3) g/cm³ and the calculated density based on the empirical formula is 2.038 g/cm³. Phosphovanadylite-Ca is isotropic with n = 1.559(2). The normalized electron microprobe analysis based upon sufficient H for charge balance and 12 molecules of zeolitic H₂O is: Na₂O 0.22, K₂O 0.55, CaO 5.58, SrO 0.10, BaO 0.21, Al₂O₃ 3.27, VO₂ 35.85, P₂O₅ 18.78, H₂O 35.44, Total 100.00. The empirical formula (based on 2 P and 28 O apfu) is: (Ca_0.75K₀₀₉Na₀₀₅Ba0.₀₁Sr₀₀₁)_∑091 [(V⁴⁺_3.27Al_0.49)_∑3.76P_2.00O_10.23(OH)_5.77] 12H₂O. The eight strongest powder X-ray diffraction lines are [d_obs in Å (m>hklm>) m>Im>]:11.04 (110) 97, 7.7881 (200) 100, 4.487 (222) 14, 3.1706 (422) 46, 2.749 (440) 32, 2.4576 (620) 14, 2.3426 (622) 15, and 1.8295 (822) 16. The crystal structure of phosphovanadylite-Ca (R₁ = 0.027 for 171 reflections with m>Fm>_o > 4m>σm>m>Fm>) contains V₄⁴⁺O₁₆ polyvanadate clusters of four edge-sharing V⁴⁺O₆ octahedra. The polyvanadate clusters are linked into a three-dimensional zeolite-like framework by sharing corners with PO₄ tetrahedra. The open space in the framework is dominated by H₂O with the equivalent of one large cation pfu sharing one of the H₂O sites. The framework is identical to that in phosphovanadylite-Ba; however, in phosphovanadylite-Ba, the dominant extra-framework cation is Ba, while in phosphovanadylite-Ca, it is Ca.