HYDROPASCOITE, Ca3(V10O28)•24H2O, A NEW DECAVANADATE MINERAL FROM THE PACKRAT MINE, MESA COUNTY, COLORADO

Hydropascoite, Ca-3(V10O28)center dot 24H(2)O, is a new mineral species (IMA2016-032) discovered in the Packrat mine, near Gateway, Mesa County, Colorado. It occurs as blades up to 2 nun 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. 1(1/2), brittle tenacity, irregular fracture, and one perfect cleavage on {001} Density (meas.) is 2.38(2) g/cm(3). Hydropascoite is biaxial (-), with alpha 1.730(5), beta 1.780(5), gamma 1.790(5) (white light); 2V (meas.) 54.1(6)degrees, and extreme dispersion. The optical orientation is X(boolean AND)a approximate to 10 degrees, Z(boolean AND) c* 20 degrees. Hydropascoite is pleocluoic, with X=bluish green, Y=orange, Z = yellowish green; X > Z > Y. Electron probe microanalysis gave the empirical formula (Ca2.69Na0.30)Sigma(2.99) (H(0.31)V(5+)10O(28)).24H(2)O, based on O = 52. Hydropascoite is triclinic, P (1) over bar, a 10.08700(19), b 11.0708(2), c 21.8112(15) angstrom, alpha=94.112(7)degrees, beta 96.053(7)degrees, y 116.398(8)degrees, V 2150.2(2) angstrom(3), and Z= 2. The strongest four lines in the diffraction pattern arc [d in angstrom(I)(hkl)]: 8.92(100)((1) over bar 10), 10.70(31)(002), 9.77(28)(010), and 7.4539(22)((1) over bar 02). The atomic arrangement of hydropascoite was solved and refined to R-1= 0.0488 for 8187 independent reflections with F > 4 sigma F. The structural unit in hydropascoite is the [V10O28](6-) decavanadate group: charge balance in the structure is maintained by the [Ca(3 center dot)24H(2)O](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, Ca-3(V10O28)center dot 17H(2)O, and its higher H2O content.