Rengeite, Sr4ZrTi4Si4O22, a new mineral, the Sr-Zr analogue of perrierite from the Itoigawa-Ohmi district, Niigata Prefecture, central Japan

Rengeite, Sr4ZrTi4Si4O22, is a new member of the perrierite-chevkinite grou p found in the jades from the Itoigawa-Ohmi district, central Japan. It is monoclinic, P2(1)/a, a = 13.97(1), b = 5.675(7), c = 11.95(1) Angstrom, bet a = 114.26(8)degrees V = 866 Angstrom (3) and Z = 2. The six strongest line s in the X-ray powder diffraction pattern are 3.12 (s) (40-3), 3.05 (vvs) ( 31-3), 2.99 (vs) (311), 2.84 (s) (020), 2.74 (s) (004), 2.20 (s) (31-5). El ectron microprobe analysis gave SiO2 22.58, TiO2 29.88, ZrO2 9.49, Nb2O5 0. 24, Ta2O5 0.07, Al2O3 0.20, FeO 0.10, CaO 0.43, SrO 34.32, BaO 0.13, La2O3 0.00, Ce2O3 0.38, Pr2O3 0.10, Nd2O3 0.29, Sm2O3 0.04, total 98.25 wt.%, cor responding to (Sr3.62Ca0.08Ce0.03Nd0.02 Ba0.01Pr0.01)(Sigma3.76) (Zr0.84Ti0 .09Al0.04Fe0.02Nb0.02)(Sigma1.01)Ti4.00Si4.11O22 On the basis of O = 22. Th e unit-cell parameters and chemical composition imply that rengeite is the Sr and Zr-analogue of perrierite or high-beta analogue of strontiochevkinit e. It is transparent, dark brown with adamantine lustre. Its streak is pale greenish brown, and no cleavage was observed. The hardness is VHN100 606-6 95 kg mm(-2) (Mohs 5-5.5). The calculated density is 4.12 g cm(-3). It is s trongly pleochroic from pale green to pale greenish brown where the REE con tents are <1 wt.% and pale violet to greenish brown where the REE contents are between 3 and 10 wt.%. It occurs as anhedral grains in close associatio n with titanite, zircon and tausonite in a pebble of blue titanian omphacit e-jadeite rock from the seashore of Oyashirazu, Ohmi Town, in a boulder of lavender-coloured Ti-bearing jadeitite from the bed of the Kotaki-gawa rive r, Itoigawa City, and in a boulder of green jade from the bed of the Hime-k awa river, Itoigawa City, Niigata Prefecture, central Japan. Rengeite is co nsidered to have crystallized by interaction between pre-existing minerals (rutile, anatase, titanite and zircon) and Sr-rich metamorphic fluid during later stage activity of high-P/T metamorphism. The name is for Mt. Renge n ear the locality and the Renge metamorphic belt where jadeitite deposits ar e found.