New data for iimoriite.

In its first reported occurrence outside of Japan, iimoriite, Y2(SiO4)(CO3), has been found in a thorite- and uraninite-bearing quartz and albite vein from Bokan Mountain on Prince of Wales Island, Alaska. It occurs as buff-tan subhedral and anhedral grains, 0.01-0.5 mm in diameter, with vitreous lustre, white streak, and H. 51/2-6. Colourless in thin section, with no pleochroism, iimoriite is biaxially negative with alpha 1.753, beta 1.824, gamma 1.830, 2Valpha (obs.) 31o, 2Valpha (calc.) 31.5o. The mineral is triclinic, space group P1 or P1, a 6.573(1), b 6.651(1), c 6.454(1) A, alpha 116.44, beta 92.34, gamma 95.63o, Z = 2, Dobs. 4.47, Dcalc. 4.56 (from Gladstone-Dale relationship), Dcalc. 4.91 (from calculated formula weight and cell volume) g/cm3. The strongest XRD lines are 2.88(100), 2.95(80), 2.78(40), 3.02(36), 2.84(35) A. Chemical analyses are tabulated. -J.A.Z.