一个呈角闪石假象的铁铝榴石

Almandine,an Emerged Hornblende Pseudomorph

本文报导了国内首见的呈角闪石假象的铁铝榴石。假象矿物产于山西省垣曲地区的绢云石英片岩中。根据其化学成分与测定、Ｘ射线粉晶分析与光学性质确定其为铁铝榴石。矿物呈红褐色，玻璃光泽，条痕无色，比重４－２５，硬度６－５～７－０ ，突起很高，Ｎ＞ １－７８０，均质性，局部显现光学异常。化学成分：ＳｉＯ２ ３６．９９，ＦｅＯ３３－６０ ，Ａｌ２ Ｏ３ ２１．６２，ＭｎＯ３ ．００ ，ＭｇＯ２ ．８９，ＣａＯ１ ．１３（ ％） 。主要粉晶线条２－５６６（１００），２－８０（５５），２－１１（４６） ；与标准铁铝榴石线条吻合。指标化后求得α为１１－５８ ｎｍ 。晶面符号及投入吴氏网后的计算结果表明，其晶形为角闪石，因而确定其为呈角闪石假象的铁铝榴石。

In 1998,we collected a red brown crystal mineral in metamorphic rock in Shanxi province, China, and our study showed that it is almandine, but emerged hornblende pseudomorph. The almandin with hornblende pseudomorph comes from quartz sericite metamorphic series of rocks. Association minerals are pyrite,sericite,quartz,muscovite,and so on. Mineral is red brown, H =6.5-7.0, G =4.25, N >1.780,and chemical compostion is following:MgO 2.89, 2.93 ;Al 2O 3 21.62,21.76;SiO 2 36.99,35.98; CaO 1.13,2. 46;MnO 3.00,2.28;FeO 33.60,34.60;Σ99.23,100.01.Crystallic chemical formula: [(Ca 0.09 Mn 0.205 )(Fe 2.27 Mg 0.34 )] 2.9 Al 2.06 [Si 2.99 O 11.97 ] or :Fe 3Al 2[SiO 4] 3 [(Ca 0.19 Mn 0.15 )(Fe 2.33 Mg 0.34 )] 3 0 Al 2[Si( 2.9 Al 0.07 ) 2.97 O 11.95 ] or:Fe 3Al 2[SiO 4] 3 The strongest X-ray lines are:2.880(55.400),2.566(100,420);2.359(45,422);2.110(46,521);1.668(62,444),1.603(50,640);1.545(57,642).Cell a =11.58?nm. The crystal goniometer data in Wuff net projection are worked out in this paper.