地开石型“老挝石”的矿物学特征

Mineralogical Characteristic of“Laos Stone”with Main Mineral Component Dickite

"老挝石"与寿山石外观极其相似,但是价格低廉且产量巨大,给寿山石的交易市场带来了严重的冲击。利用偏光显微镜、X射线粉晶衍射仪、傅里叶红外光谱仪、拉曼光谱仪、扫描电子显微镜、电子探针对"老挝石"的矿物学特征进行了详细的分析。结果表明:(1)不同颜色的"老挝石"主要矿物组成相同,以地开石(2M1型)为主,含有少量珍珠陶石和高岭石,地开石整体结晶程度差,偶见假六方片状,颗粒大小不一;(2)扫描电子显微镜和拉曼光谱显示,"老挝石"中次要矿物有赤铁矿、金红石、长石和硫磷铝锶石。老挝石中大部分赤铁矿结晶形态良好,呈现四边形或者六边形的结晶外形,少量赤铁矿呈浸染状包围形态规则的赤铁矿、长石,或分布在裂隙中,颜色富集,红色调加深,"老挝石"中"萝卜纹"的光泽、透明度与基质不同,呈现网脉状分布,矿物成分为硫磷铝锶石;(3)电子探针结果表明,红色"老挝石"中Fe质量分数较高,浸染状赤铁矿可能是导致"老挝石"呈现红色的主要原因。

＂Laos stone＂is very similar to ＂Shoushan stone＂in appearance.However,the price of＂Laos stone＂is much lower than that of＂Shoushan stone＂since its large production,which has brought a severe impact to the market of＂Shoushan stone＂.Optical microscope,Fourier transform infrared spectrometer（FTIR）,X-ray diffraction（XRD）,laser Raman spectroscopy（LRM）,scanning electron microscopy（SEM）and electron probe micro analysis（EPMA）were applied to study its mineralogical characteristics.The XRD results showed that the main mineral component of samples in different colour（red,black and white）is dickite（type 2 M1）.The crystallinity of dickite is poor,while some dickites forming hexagonalplate with different sizes.Minor nacrite and kaolinite are also detected.SEM and LRM testing results revealed secondary mineral components in＂Laos stone＂include hematite,rutile,svanbergite and feldspar.Svanbergite is the main composition of＂radish striae＂and occurs in fragments or net veins,whose transparency and luster are different from the basic part of＂Laos stone＂.The EPMA result showed that the Fe is enriched in the red＂Laos stone＂.A majority of hematite shows good crystallinity with tetragon and hexagon appearance.The hematite being disseminated structures commonly surrounds the hematite crystal or distributes in the cracks of＂Laos stone＂and deepens the red colour.