Mineralogical characteristics and coloration mechanism of prehnite in basaltic druse from southern sichuan and northern Yunnan are investgated by optical microscopy,X-ray power analysis,scanning electron microscopy,electron probe microanalysis,ultraviolet-visible-near infrared spectrophotometer,etc.Prehnite in basaltic druse from Puge County shows bluish yellow green and light yellow green in two different colors.The morphology of single crystals is mainly plate-like,pinacoid c {001 } and orthorhombic prism m{110} is developed,and pinacoid a{ 100} is not obvious.The aggregates of prehnite are scallop shape and grape-like shape.The components of prehnite are A12 O3,SiO2,CaO,FeO,Fe2 O3,with a small amount of Cr2 O3.Color of Zhaotong prehnite is light blue green,yellow green,and bright yellow green,single crystals is mainly columnar crystal.The common forms are orthorhombic prism m { 110 },pinacoid a { 100 } and c { 001 }.Pinacoid c { 001 } are shown in the largest area,followed by the pinacoid a { 100 },while orthorhombic prism m { 110 } in prehnite crystal are shown in the smaller area.The aggregates of Zhaotong prehnite are mainly of lantern-shaped,and there is no Cr2O3 in the chemical composition of Zhaotong prehnite.This study shows the color of prehnite mainly caused by the crystal field splitting of the colored ions,such as Fe2+,Fe3+,Cr3+,and so on.The hole formed by the substitution of the isomorphism between different valence cations outside the silicon oxygen skeleton has some influence on the color of the prehnite.The deepening of prehnite color is directly proportional to the content of iron (or iron and chromium),and there is an increase of amount of chromium which decreased prehnite crystal transparency.%利用光学显微镜和X射线粉末衍射仪、扫描电镜、电子探针及紫外-可见-近红外分光光度计等现代测试仪器设备,对川南普格和滇北昭通玄武岩晶洞中的葡萄石及其晶体聚集体的矿物学特征开展系统研究,探讨了葡萄石的颜色成因.普格葡萄石有微蓝的黄绿色和浅黄绿色两种不同的颜色,单晶体主要为板状,平行双面c{001}和斜方柱m{110}较发育,平行双面a{100}基本不发育,聚集体呈扇贝状、葡萄状,成分中除了Al2O3、SiO2、CaO、FeO、Fe2O3外,还有少量的Cr2O3.昭通葡萄石表现为浅蓝绿色、浅黄绿色,甚至鲜黄绿色,单晶体以板柱状为主,常见单形为斜方柱m{110}、平行双面a{100}及c{001},平行双面c{001}最发育,其次是平行双面a{100},斜方柱{110}出露的面积较小,聚集体主要为灯笼状,成分中不含Cr2O3.葡萄石的颜色主要是Fe2、Fe3+、Cr3+等致色离子的晶体场分裂所引起,硅氧骨干外异价阳离子之间的类质同像替代所形成的空穴对葡萄石的颜色也有一定的影响.葡萄石颜色随铁(或铁和铬)含量的增加而加深,铬含量的增大有降低葡萄石晶体透明度的趋势.
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