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A new Sr-Ti hydrous silicate mineral was found in albitite cutting serpentinite at Ohmi, Niigata Prefecture, central Japan. It occurs as aggregate of fibrous crystals of light pink in color. The mineral is mono clinic with a=10.958 A ; b=7.778 A ; c=7.799 A, p=100•‹54', space group P21/ m. Crystals are elongated along b-axis, density 3.38; hardness 3.5, weak pleochroism, a=1.849, r=1.715. Chemical analysis gave Si02 34.79, Ti203 10.27, Fe203 0.20, SrO 47.37, H20 6.68, Total 99.31. The chemical formulae of the mineral is Sr3TiSi4012(OH)•E2H2O. In autumn of 1971, a new strontium-titanium hydrous silicate mineral was found in an amphibole-quartz-albitite dike cutting serpen tinite in Ohmi, Niigata Prefecture, Central Japan. It occurs rarely as aggregates of very fine-grained crystals or occasionally spherulitic aggregates of radially arranged crystals in interstitial parts of albite aggregates. They are pink to pinkish brown in colour and reach about 0.2 mm across in maximum. The associated minerals include blue fibrous amphibole of magnesioriebeckitic composition, quartz, albite, phlogopite, benitoite and a joaquinite-like mineral which is often included within the aggregates. Because of its natures of aggregate, accurate measurement of hardness is made with difficulty, Mohs' hardness being about 3.5. The streak is white. Specific gravity is 3.394g/cm3(calc.) and 3.38 (meas.) respectively. Under the microscope, the aggregates have M. KOMATSU, K. CHIHARA and T. MIZOTA 299 fibrous or feather-like texture and show wavy arrangement as a whole, but its columnar forms are observed along the margins of aggregate. The individual grain size forming aggregates is less than 5 microns in width and 10 microns in length. X-ray single crystal study employing four circle goniometer shows it to be monoclinic, possible space group P21 or P21/m (the latter is preferred from its structural analysis), a=10.958±0.0016 A, b=7.778±0.0010 A, c=7.799±0.007 A, (3=100•‹54'•}0.04'. X-ray powder data are satisfactorily indexed by this cell (Table 1). It is optically Table 1. X-ray powder data for a new Sr-Ti hydrous mineral from Ohmi. Cu Kƒ¿ radiation with Ni-filter 3 00 Short Communication biaxial with b=Z and a=Y. Because of its extremely small grain size and elongated nature to [010], 2V, optical sign, and c ?? Y are not determined. Refractive indices are a=1.649±0.003, and r= 1.715±0.003. Pleochroism is very weak changing from nearly colour less to light pink. Cleavage is parallel to (100), perfect. As shown in Table 2, the chemical analysis shows Si02, Ti02, SrO and H2O as essential constituents. Among them, SrO content is very high, this mineral being the silicate mineral richest in strontium ever known. After the reference of the result of crystal structure analysis, the ideal formula is given as Sr3TiSi4012(OH)•E2H2O. Two molecules are contained in the unit cell. The charge number of Ti ions was determined to be +3, considering about the hydrogen content and the result of crystal structure analysis. The faint pink colour of this mineral may illustrate the existence of 3d electrons Table 2. Chemical composition of Sr-Ti hydrous silicate mineral from Ohmi (1) Analysed by E. P. M. A. (a): not detected by E. P. M. A. H2O+: weighed loss of ignition above 110°C H20-: weighed loss at 110°C (2) Calculated from the ideal formula Sr3TiSi4012(OH)•E2H2O (3) Cation content in unit cell based on Si=8 (4) Ideal cation content M. KOMATSU, K. CHIHARA and T. MIZOTA 301 in Ti" ions, because other ions are not effective in color except for the small amount of iron contained. But the valency of titanium of the mineral can not be settled clearly. Detail discussions on the numbers of OH and H20, and valency of Ti ions will be done else where. The authors wish to express their hearty thanks to Drs. A. Kato, K. Sakurai of National Science Museum and Prof. K. Yagi of Hokkaido University for their valuable advice and discussion. Their thanks are also due to Dr. Y. Yamaguchi of Kyoto University who kindly determined the indices of refraction of mineral concerned. REFERENCES MIZOTA, T., KOMATSU, M. and CHIHARA, K. (1973). Miner. Journ. 7, 302305. Received June 27, 1973

A New Strontium-Titanium Hydrous Silicate Mineral from Ohmi, Niigata Prefecture, Central Japan