“昌化朱砂石”的宝石学特征

Gemmological Characteristic of Clay Mineral Jade(“Changhua Zhushashi”)

浙江昌化是我国重要的图章石产地,产出有种类丰富、色彩缤纷的图章石,针对商业名为“昌化朱砂石”的材料,利用偏光显微镜、X射线粉末衍射仪、红外光谱仪、拉曼光谱仪、扫描电子显微镜对其宝石学特征进行研究。结果表明,“昌化朱砂石”为隐晶质结构的粘土矿物质玉,主要由地开石、高岭石及赤铁矿组成,其中地开石、高岭石多为半自形-他形的不规则片状,粒径为几微米到十几微米,集合体在三维空间呈无序排列。根据结晶形态的不同,可将赤铁矿分为两类:(1)粒径30~400μm的黑色六边形片状赤铁矿,在抛光成品的表面可显示砂金效应;(2)粒径不超过0.5μm的细粒赤铁矿集合体,这类赤铁矿使“昌化朱砂石”呈现褐红色。推测这两类赤铁矿先后形成于热液蚀变及接触交代阶段。“昌化朱砂石”中还含有少量的黄铁矿及石英。

Changhua,Zhejiang Province is an important place of seal stone production in China.There are various kinds of colourful seal stones produced in Changhua,Zhejiang Province.The object of this study is maroon-red“Changhua Zhushashi”.Polarizing microscope,Fourier transform infrared spectrometer(FTIR),X-ray powder diffractometer(XRD),laser Raman spectroscopy(LRM),and scanning electron microscopy(SEM)were applied to study the gemmological characteristics of the samples.The results showed that the maroon-red“Changhua Zhushashi”is clay mineral jade with cryptocrystalline structure,and is composed of dickite,kaolinite and hemitate.Crystals of dickite and kaolinite are mostly irregular subhedral to anhedral sheet,with poor orientation,and particle size ranging from a few microns to a dozen microns.According to the crystal morphology,hematite is characterized by two crystalline forms:The first hematite type is a regular hexagonal crystal size of 30-400μm,which can form optical phenomena on the surface of polished finished products;The second is aggregation of tiny particles about 0.5μm in size,and its colour is maroon.It is speculated that these two crystalline forms of hematites are formed in the stage of hydrothermal alteration and contact metasomatism respectively.Furthermore,maroon-red“Changhua Zhushashi”contains pyrite and quartz.