Abstract

Burroite, Ca2(NH4)2(V10O28)·15H2O, is a new mineral species (IMA2016-079) discovered in the Burro mine, Slick Rock district, San Miguel County, Colorado, U.S.A. (38°2′42″N 108°53′23″W). The mineral is found as orange-yellow, somewhat flattened prisms up to 2 mm in length occurring on a montroseite- and corvusite-bearing sandstone. Burroite has yellow streak, vitreous luster, brittle tenacity, a Mohs hardness of 1½–2, good cleavage on {001}, and irregular fracture. The measured density is 2.43(2) g·cm–3. The partially determined optical properties are α = 1.764(3), β = n.d., γ > 1.81, orientation Xa, Y probably ≈ c*. Electron probe microanalysis gave the empirical formula (based on 43 O apfu) [Ca1.88(NH4)1.82Na0.18]Σ3.88(H0.23V5+10O28)·15H2O. Burroite is triclinic, space group forumla, with a 8.779(2), b 10.311(2), c 12.060(2) Å, α 96.740(4)°, β 107.388(5)°, and γ 114.439(6)°, and V = 911.2(3) Å3. The strongest four lines in the diffraction pattern are [d in Å(I)(hkl)]: 11.06(100)(001), 9.02(46)(010), 8.10(21)forumla, and 7.71(94)forumla. The atomic arrangement of burroite was solved and refined to R1 = 0.0946 for 2711 independent reflections with F > 4σ(F). The structural unit in burroite is the [V10O28]6– decavanadate group; charge balance in the structure is maintained by the [Ca2(NH4)2·15H2O]6+ interstitial complex. Linkage between the structural unit and the components of the interstitial complex is principally by hydrogen bonding. The mineral is named for the Burro mine in which it was found.

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