Rengeite, Sr4ZrTi4Si4O22, is a new member of the perrierite–chevkinite group found in the jades from the Itoigawa-Ohmi district, central Japan. It is monoclinic, P21/a, a = 13.97(1), b = 5.675(7), c = 11.98(1)Å, β = 114.26(8)°, V = 866 Å3 and Z = 2. The six strongest lines 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). Electron 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.%, corresponding to (Sr3.62Ca0.08Ce0.03Nd0.02Ba0.01Pr0.01)∑3.76 (Zr0.84Ti0.09Al0.04Fe0.02Nb0.02)∑1.01Ti4.00Si4.11O22 on the basis of O = 22. The unitcell parameters and chemical composition imply that rengeite is the Sr and Zr-analogue of perrierite or high-β analogue of strontiochevkinite. It is transparent, dark brown with adamantine lustre. Its streak is pale greenish brown, and no cleavage was observed. The hardness is VHN100 606–698 kg mm−2 (Mohs 5–5.5). The calculated density is 4.12 g cm−3. It is strongly pleochroic from pale green to pale greenish brown where the REE contents 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 association with titanite, zircon and tausonite in a pebble of blue titanian omphacite-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 river, Itoigawa City, and in a boulder of green jade from the bed of the Hime-kawa river, Itoigawa City, Niigata Prefecture, central Japan. Rengeite is considered 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 near the locality and the Renge metamorphic belt where jadeitite deposits are found.

Coexisting Ba-rich (Cn56–59Or40–42Ab2An0–1) and Ba-poor (Cn7–15Or83–92Ab1–3An0–1) feldspars were found in a jadeitite collected from the Itoigawa-Ohmi district in the Renge high-P/T-type metamorphic belt, Japan. There is an apparent compositional gap in these barian feldspars at Cn15–56 in the ternary system BaAl2Si2O8–KAlSi3O8–NaAlSi3O8. Barian feldspars occur as interstitial phases between subhedral to euhedral jadeite and prehnite, and sometimes cut a jadeite crystal. The occurrence of barian feldspars combined with the texture and mineral assemblages of the host jadeitite suggest that barian feldspars were formed from residual fluids after the formation of jadeite and prehnite from primary aqueous fluids at low-T conditions (<350°C) and pressure of ~0.6 GPa. The Ba content in the residual fluids would increase locally during the formation of jadeite because Ba is incompatible with clinopyroxene. This study supports the suggestion that Ba-rich minerals are not uncommon in jadeitites and albitites/metasomatized rocks that occur as tectonic blocks in serpentinite-matrix mélanges. Barium is an important minor element in metasomatizing fluids related to the formation of jadeitites and might have been derived from subducted oceanic crust at the beginning of the subduction.

Itoigawaite, SrAl2Si2O7(OH)2·H2O, is a new member of the lawsonite group found in the Itoigawa-Ohmi district, central Japan. It is orthorhombic, Cmcm, a = 6.031(2), b = 8.945(2), c = 13.219(4) Å, Z = 4. The strongest lines in the X-ray powder diffraction pattern are 4.68 (s) (111), 4.26 (vs) (021), 3.31 (vs) (113), 2.75 (vs) (114, 202), 2.68 (vvs) (130), 2.63 (s) (131), 2.50 (s) (220, 203, 132), 2.45 (s) (221). Electron microprobe analysis gave SiO2 32.98, TiO2 0.87, Al2O3 27.67, Fe2O3 0.39, MgO 0.27, CaO 0.45, SrO 27.71, H2O (diff.) 9.66, total 100.00 wt.%, corresponding to (Sr0.97Ca0.03Mg0.02)Σ1.02 (Al1.97Ti0.04Fe0.02)Σ2.03Si1.99H3.89O10 on the basis of O = 10. It is transparent, blue in colour with vitreous lustre. The streak is white and the cleavage good in one direction. The hardness is 5–5.5. The calculated density is 3.3 g cm−3. It is colourless in thin section and optically biaxial positive with α = 1.664 (2), β = 1.674 (2), γ = 1.688 (2) and 2V(calc.) = 81°. It occurs in a thin veinlet cutting a lavender-coloured Ti-bearing jadeitite. The veinlet includes irregularly-shaped aggregates composed of minute tabular crystals of itoigawaite up to 50 µm across and minute jadeite crystals with interstitial natrolite aggregates. Itoigawaite is considered to be crystallized from fluid during later stage activity of high-P/T metamorphism. The name is for the locality.