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1 Fossa Magna Museum, Itoigawa, Niigata 941-0056, Japan
2 National Science Museum, Hyakunin-cho, Shinjuku, Tokyo, 169-0073, Japan
3 Kotaki Bussan Co., Itoigawa, Niigata 949-0462, Japan
* e-mail address: m{at}e-hisui.com (Hiroshi Miyajima)
Matsubaraite, Sr4 Ti5(Si2 O7)2 O8, is a new member of the perrierite-chevkinite group found in the jadeitite from the Itoigawa-Ohmi district, central Japan. It is monoclinic, P21/a (pseudo C2/m). a = 13.848(7), b = 5.626(2), c = 11.878(6) Å, ß = 114.19(4)°, V = 844 Å3 and Z = 2. The six strongest lines in the X-ray powder diffraction pattern are 3.16 (70) (400), 3.09 (95) (–403), 3.01 (90) (–313). 2.96 (95) (311), 2.71 (100) (004). 2.17 (90) (–421). Electron microprobe analysis gave SiO2 22.60, TiO2 39.06, SrO 38.84 total 100.50 wt.%, corresponding to Sr3.92Ti5.11 Si3.93O22 on the basis of O = 22. The crystal structure analysis (R = 0.0372) revealed that the space group is pseudo C2/m, and that matsubaraite is Sr and Ti-analogue of perrierite-(Ce), Ce4Fe2Ti3 (Si2 O7)2O8, or Zr-free analogue of rengeite, Sr4ZrTi4 (Si2 O7)2 O8. It is transparent, grey with blue tint with adamantine luster. Streak is white, cleavage not observed. The hardness is VHN100 681-743 kg mm–2 (Mohs' 5.5). The calculated density is 4.13 g cm–3. It occurs as long prismatic euhedral to subhedral crystal with interstitial natrolite in a boulder of lavender-colored Ti-bearing jadeitite from the bed of the Kotaki-gawa river, Itoigawa City, Niigata Prefecture, central Japan. Matsubaraite is considered to have crystallized during later stage activity of high-P/T metamorphism. The mineral is named after Dr Satoshi Matsubara of department of Geology, National Science Museum in recognition of his works on strontium dominant minerals from Japan.
Key-words: matsubaraite, new mineral, strontium, perrierite group, jadeite, Itoigawa-Ohmi district, crystal structure..
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