Hydropascoite, Ca3(V10O28)·24H2O, is a new mineral species (IMA2016-032) discovered in the Packrat mine, near Gateway, Mesa County, Colorado. It occurs as blades up to 2 mm in length on asphaltum associated with montroseite- and corvusite-bearing sandstone. Hydropascoite is dark yellow green, with a pistachio green streak, vitreous luster, Mohs hardness of ca. 1½, brittle tenacity, irregular fracture, and one perfect cleavage on {001}. Density (meas.) is 2.38(2) g/cm3. Hydropascoite is biaxial (–), with α 1.730(5), β 1.780(5), γ 1.790(5) (white light); 2V (meas.) = 54.1(6)°, and extreme dispersion. The optical orientation is X ^ a ≈ 10°, Z ^ c* ≈ 20°. Hydropascoite is pleochroic, with X = bluish green, Y = orange, Z = yellowish green; X > Z > Y. Electron probe microanalysis gave the empirical formula (Ca2.69Na0.30)Σ2.99(H0.31V5+10O28)·24H2O, based on O = 52. Hydropascoite is triclinic, forumla, a 10.08700(19), b 11.0708(2), c 21.8112(15) Å, α 94.112(7)°, β 96.053(7)°, γ 116.398(8)°, V 2150.2(2) Å3, and Z = 2. The strongest four lines in the diffraction pattern are [d in Å(I)(hkl)]: 8.92(100)(forumla), 10.70(31)(002), 9.77(28)(010), and 7.4539(22)(forumla). The atomic arrangement of hydropascoite was solved and refined to R1 = 0.0488 for 8187 independent reflections with F > 4σF. The structural unit in hydropascoite is the [V10O28]6– decavanadate group; charge balance in the structure is maintained by the [Ca3·24H2O]6+ interstitial complex. The three Ca polyhedra in the interstitial complex are not polymerized. Linkage between the structural unit and the components of the interstitial complex is principally by hydrogen bonding. In addition to the extensive hydrogen bonding, three oxygen atoms of the structural unit bond directly to calcium atoms of the interstitial complex. The mineral is named to recognize its chemical and structural similarity to pascoite, Ca3(V10O28)·17H2O, and its higher H2O content.

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