Gainesite, sodium zirconium, beryllophosphate; a new mineral and its crystal structure

Gainesite, hypothetical end-member Na₂Zr₂[Be(PO₄)₄], a = 6.567(3), c = 17.119(5)Å, Z = 2, tetragonal, space group I4₁/amd, is a new species from the Nevel (Twin Tunnels) pegmatite, Newry, Oxford County, Maine. Crystals occur as up to 1 mm simple tetragonal bipyramids with p{lll} dominant. The color is delicate pale bluish lavender, hardness = 4 on Molls’ scale, luster vitreous, conchoidal fracture, specific gravity 2.94. It is uniaxial (+), ω = 1.618(2), ε = 1.630(2). The mineral occurs in small crevices in cleavelandite associated with monoclinic roscherite and minor eosphorite. It is named in honor of Richard V. Gaines.

R = 0.055 for 1072 independent reflections. Eight atoms occur in the asymmetric unit of structure and five of these are disordered. Be, P, and 0(3) are half-occupied while Na(1) and Na(2) are each approximately one-eighth occupied. The structure is based on an open framework of composition [^[6]Zr₂^[4]Be^[4]P₄O₁₆]²⁻. The [BeP₄O₁₆]¹⁰⁻ pentameric cluster is reminiscent of the zunyite, [Si₅O₁₆]¹²⁻ anionic fraction.

Bond distance averages are ^[6]Na(1)−O = 2.49, ^[12]Na(2)−O = 3.32, ^[6]Zr−O = 2.062,

^[4]Be−O = 1.621 and ^[4]P−O = 1.512Å. Smaller alkalies (Li⁺, Na⁺) appear to partition in Na(1) and larger alkalies (Na⁺, K⁺, Rb⁺, Cs⁺) appear to partition in Na(2).