电子微探针-X射线衍射-扫描电镜研究老挝石岩石矿物学特征

新近发现的老挝石因与寿山石多个品种高度相似,给老挝石的科学定名和印材质量评价带来困难。本文采用常规宝玉石学测试结合电子微探针(EPMA)、X射线粉晶衍射(XRD)以及扫描电镜(SEM)等矿物谱学分析测试方法,系统解析其化学成分、矿物组成及显微结构特征。结果表明,老挝石由高岭石亚族矿物多型组成,其中主要为高岭石、地开石及其过渡矿物,少量为珍珠陶石。红、黄色老挝石颜色与铁含量呈正相关性,表明铁元素可能为老挝石常见红、黄两色的主要致色原因。老挝石主要组成矿物晶体以不规则鳞片状或假六方片状为主,其粒径越细小、镶嵌越紧密,相应表现为质地细腻和篆刻工艺性能优异,作为印章石的工艺价值也就越高。老挝石的密度(2.58~2.60 g/cm3)及折射率(1.561~1.570)等常规宝石学特征均与地开石型寿山石较为一致,其中颜色鲜艳、结构细腻者可作为优质的篆刻印材新资源。

Study on Petrological and Mineralogical Characteristics of Laos Stone by EPMA-XRD-SEM

Since the newly-discovered Laos stones have highly similar appearances with Shoushan stones,it is difficult to correctly identify and evaluate them.Electron Microprobe(EPMA),X-ray Powder Diffraction(XRD) and Scanning Electron Microscopy(SEM) were used to study the chemical composition,mineral components,and microstructure of the Laos stone.Results show that the Laos stone is mainly composed of kaolinite,dickite and their transitional minerals with minor nacrite.There is a positive correlation between the red color and the yellow color and the amount of impurity element Fe,which indicates that these colors are possibly caused by Fe.Laos stone's crystals are mostly irregular platy or uninterrupted pseudo-hexagonal platy.The smaller size the crystals have,the worse porosity of its crystals,leading to the finer texture and better seal engraving experience and therefore a higher value.The density(2.58-2.61 g/cm³),refractive index(1.559-1.570) as well as other conventional gemological characteristics of Laos stone are similar to todickite-type Shoushan stones.It is suggested that Laos stone with bright color and fine texture should be used as a new source of high-quality seal stones.