Botuobinskite and mirnyite, two new minerals of the crichtonite group included in Cr-pyrope xenocrysts from the Internatsionalnaya kimberlite

Abstract

Two new mineral species of the crichtonite group -botuobinskite, ideally SrFe 2+ (Ti 4+ 12Cr 3+ 6)Mg2[O36(OH)2], and mirnyite, ideally SrZr(Ti 4+ 12Cr 3+ 6)Mg2O38, occur as inclusions in mantle-derived Cr-pyrope xenocrysts from the Internatsionalnaya kimberlite pipe, Mirny field, Siberian craton. Botuobinskite forms needle-and blade-like acicular crystals up to 1 mm in length and up to 30 µm in diameter, a large platy inclusion (700x700x80 µm) and roughly isometric grains (up to 80 µm), while mirnyite occurs as needle-and blade-like elongated inclusions (up to 1 mm). Both minerals are jet-black, opaque and exhibit metallic lustre. In plane-polarised incident reflected light, botuobinskite and mirnyite are greyish-white with a weak brownish tint. Between crossed polars, the new species show distinct anisotropy in shades of bluish grey to greenish-brown. Neither bireflectance nor pleochroism is observed. Calculated densities for botuobinskite and mirnyite are 4.3582(5) and 4.3867(3) gm/cm 3 , respectively. The crystal structures of botuobinskite and mirnyite have been refined (R = 0.0316 and 0.0285, respectively) from single crystal X-ray diffraction data. The minerals are trigonal, crystallize in the space group R−3 (No. 148) and are isostructural with other members of the crichtonite group.

Haitaite‐(La), LaU4+Fe3+2(Ti13Fe2+4Fe3+)Σ18O38, a New Member of the Crichtonite Group

“…The compositions of both original haitaite-(La) and (6) Hey et al, 1969;(7) Gatehouse et al, 1979;(8) Orlandi et al, 1997;(9) Bittarello et al, 2014;(10) Orlandi et al, 2004;(11) Grey and Gatehouse, 1978;(12) Haggerty et al, 1983;(13) Zhang et al, 1988;(14) Gatehouse et al, 1978;(15) Kelly et al, 1979;(16) Biagioni et al, 2014;(17) Gatehouse et al, 1983;(18) Mills et al, 2012;(19) (20) Foord and Sharp, 1984;(21) Dragila, 1990;(22) Chukanov et al, 2020;(23) Rezvukhin et al, 2020. heated haitaite-(La) were considered. The results of electron microprobe analyses (EMPA, JXA-8100; WDS, 20 kV; 20 nA; beam diameter 2μm) of original haitaite-(La) (n = 15) and heated haitaite-(La) (n = 10) are summarised in Table 3.…”