New data for iimoriite.

Iimoriite, Y2(SiO4)(CO3), has been identified from Bokan Mountain on Prince of Wales Island, Alaska; it is the first reported occurrence of this mineral outside of Japan. The mineral occurs in a thoriteand uraninite-bearing quartz and albite vein. Iimoriite occurs in subhedral to anhedral grains that range from 0.01 to 0.5 mm in diameter. The mineral is buff-tan and has a Mohs hardness of 5.5 to 6., D: 4.47, D. : 4.56 (using the Gladstone-Dale relationship), and D" = 4.91 (using calculated formula weight and cell volume). The luster is vitreous, and the streak is white. The mineral shows at least one good cleavage and does not fluoresce under either short-wave or long-wave ultra-violet light. It is slightly soluble in cold HCl. Optically, iimoriite is biaxial negative w i t h r e f r a c t i v e i n d i c e s c r : 1 . 7 5 3 , P : 1 . 8 2 4 , y : 1 . 8 3 0 ; y q : 0 . 0 7 7 ; 2 V ^ ( m e a s . ) : 3 1 ' ' 2V*(calc.): 31.5". The optic plane is parallel to a cleavage direction. It is colorless aqd shows no pleochroism in thin section. The mineral is triclinic with space group Pl or Pl, and least-squares refinement of 60 reflections from X-ray powder data yields: a : 6.573(l), b : 6 . 6 5 1 ( l ) , c = 6 . 4 5 4 0 ) ] r , a = 1 1 6 . 4 4 " , F : 9 2 . 3 4 " , y : 9 5 . 6 3 " , V : 2 5 0 . 3 0 ( 0 A 3 . Z : 2 . The eight strongest lines in the X-ray powder pattern a1e (d in A. inrenlity, ftkD 2.88(100) (002 and lll), 2.9s(80)(20_l), 2.78(40)(022), 3.02(36X210), 2.84(35)(12r'), 2.70(29)(210), 3.30(27)(02r), and 4.54(25)( 10 I ). Iimoriite was analyzed by a combination of several analytical methods. A calculated structural formula for the Bokan Mountain iimoriite (on the basis of 7 oxygens) is: (Yr.++ Las.0o2Ce6.063Prs.662Nd6.soaSmq.0o6Gde.saEus.0o2TboozDyo11Ho6.s3Ere11Tms.s1 Ybssg Lus se Fe*3q.sz Ca o ol)r.ss Si l.12O4[(CO r)o.sr(HzO*)o.ra]r.os.