一个新的铋、铬氧化物──铬铋矿

A NEW OXIDE OF BISMUTH AND CHROMIUM──CHROMBISMITE

铬铋矿（Bi16．006Cr0．997O27）是在陕西省洛南县驾鹿金矿床中发现的一种新矿物。该矿物通常呈不规则状微细晶集合体，柱状小晶体大小在0．005mm×0．002mm～0．05mm×0．025mn。之间，集合体大小约0．01～0．5mm。呈桔黄或黄棕色，性脆，半透明，条痕棕黄色，金刚光泽，具不完全解理；一轴晶，正光性。实测密度为9．80（3）g／cm3。计算密度9．85（1）g／cm3。维氏硬度95．8～128kg／mm2，摩氏硬度3～4。折射率ω＝2．50（2），ε＝2．55（2）。15个电子探针平均成分Bi2O3为97．25％，CrO3为2．6％，总和99．95％，化学式：Bi16．006Cr0．997O27，理论式：Bi16CrO27。X射线粉晶衍射主要强线d（I）（hkl）为：0．319（100），（123）；0．273（40），（310）；0．198（40），（316）；0．1932（20），（420），0．1715（30），（219）；0．1655（55），（503，·433）。根据指标化求得铬铋矿为四方晶系，可能的空间群为I4，I4或I4／m；a＝0．8649（3）um，c＝1．724（1）nin，c／a＝1．9933；V＝1．2896（6）nm3，Z＝2。1－Kp／Kc＝0．025。铬铋矿作为新矿物及其命名已被国际矿物学协会新矿物和矿物命名委员会批准通过，其样品存放中国地质博物馆。

Chrombismite (Bi16.006,Cr0.997O27 ) is a new mineral discovered in the Jialu gold mine, LuonanCounty, Shaanxi Province. The mineral occurs as irregular fine-grained aggregates. Small columnarcrystals measure about 0.005mm×0.002mm ~0.05mm ×0.025mm in size and the aggregatesabout 0. 01 ~0. 5mm in size. Chrombismite is yellowish-brown in color, brittle, translucent, brown-ish-yellow in steak, adamantine in luster and imperfect in cleavage. The crystal is uniaxial positivewith ω= 2. 50 (2), ε= 2.55 (2). The measured density is 9. 80 (3) g/cm3 and the calculated oneis 9. 85 (1 ) g/cm3. Its Vickers hardness is 95. 8~ 128kg/mm2 and Mohs hardness is 3~4. The aver-age composition of 15 samples hy microprobe analysis is Bi2O3 97. 25wt %, CrO3 2. 6 wt %, totalling99. 85 wt % . The formula is Bi16.006 Cr0.997 O27 and the ideal formula is Bi16 CrO27. Principal lines in theX-ray powder pattern Ld (1) (hkl)] are: 0. 319 (100), (123); 0. 273 (40), (310); 0.198(40), (316); 0. 193 2 (20), (420); 0. 171 5 (30), (219); 0.165 5 (55), (503, 433). lt wasdetermined that chrombismite is tetragonal, with aposslble space group of I4, I4 or I4/m; a = 0. 8649 (3) nm, c＝1. 724 (1) nm, c/a=1. 993 3; V= 1. 289 6 (6) nm3, Z=2, and l-Kp/Kc=0.025Chrombismite and its name have been approved by the Commission on New Minerals and Mineral Names, IMA. The holotype specimen of chrombismite is stored at the Geological Museum ofChina, Beijing.