陕西紫绿玛瑙的环带致色机理研究  

Colouration Mechanism of Circular Bands of Purple-Green Agate from Shaanxi Province

作　　者：吕雨姗 陈涛[1] 陈倩 LYU Yushan;CHEN Tao;CHEN Qian(Gemmological Institute,China University of Geosciences,Wuhan 430074,China;Shaanxi Experimental Center of Geological Survey,Xi’an 710000,China)

机构地区：[1]中国地质大学(武汉)珠宝学院,湖北武汉430074 [2]陕西省地质调查实验中心,陕西西安710000

出　　处：《宝石和宝石学杂志（中英文）》2024年第S01期115-118,共4页Journal of Gems & Gemmology

基　　金：陕西省自然科学基础研究计划资助项目(2022JQ-258)。

摘　　要：2015年,陕西省洛南县境内新发现一种特色石英质玉——紫绿玛瑙,以红色、绿色、紫色最为典型,现有文献^([1-3])主要针对“红心绿边”型紫绿玛瑙开展过宝玉石学特征和颜色成因分析,而关于具有橙红-白-绿等多色环带的紫绿玛瑙的宝石学特征以及形成条件的资料较少。本研究选择陕西省洛南县境内麻花沟、十八盘、学沟、朱家洼等矿区产出具有代表性的紫绿玛瑙样品共16块,对其进行常规宝石学观察、偏光显微镜观察以及拉曼光谱、红外光谱、紫外光谱和扫描电子显微镜等测试,对其宝石学特征、矿物组成及其环带致色成因进行了分析。本文紫绿玛瑙样品(图1)的主要矿物组成为石英,粒度大多约为0.01 mm,含量在90%以上,同时含有少量的粘土矿物、暗色金属矿物以及碳酸盐矿物等。其中,红色杂质矿物呈细小点状或浸染状分布,粒度微细(1~20μm);绿色杂质矿物呈片状、纤维状分布。红外透射光谱(溴化钾压片法)结果显示,样品显微结构的空隙中还存在不同程度的分子水。红色、紫色、无色样品在3628 cm^(-1)处基本无结构水特征峰,绿色样品在3628 cm^(-1)处呈现显著吸收峰,推测其含水矿物所含结构水导致此处吸收。拉曼光谱测试发现极少部分α-石英光谱在508 cm^(-1)处可观察到较弱的斜硅石信号,这与现有文献中紫绿玛瑙中不存在斜硅石的结论不同。在具有橙红-白-绿典型环带结构样品中,橙色中心主要杂质矿物为赤铁矿,还存在大量表面附着赤铁矿的白云石,呈橘红色外观,这一定程度上也造成环带中心区域呈现橙色;中心到边缘过渡的无色环带内存在大量粒度0.01~0.02 mm的锐钛矿;外层绿色部分主要杂质矿物为绿泥石、绢云母,部分样品中还观察到少量钠角闪石;样品QZ-1黄色部分主要成分为白云石。红色、紫红色样品的紫外-可见光谱出现了赤铁矿的特征峰[4]以及�In 2015,the characteristic quartz jade-purple-green agate,was discovered in the territory of Luonan county,Shaanxi Province,whose typical colour is red,green,and purple.The existing literature mainly focused on the gemmological characteristics and colour genesis of the“red core and green belt”type of purple-green agates[1-3].However,there are still fewer studies on the gemmological characteristics and formation conditions of the purple-green agate with a multicoloured band of orange-white-green.There are still fewer studies on the gemmological characteristics and formation conditions of purple-green agate.In this study,a total of 16 representative samples from the mining areas of Mahuagou,Shibapan,Xuegou,and Zhujiawa in Luonan county,Shaanxi Province,were selected.The gemmological characteristics,mineral compositions,coloration genesis of the ring-banding of the purple-green agate samples were studied using conventional gemmological tests,polarizing microscope,Raman spectrometer,infrared spectrometer,ultraviolet spectrometer,and scanning electron microscope.The main mineral composition of purple-green agate(Fig.1)is quartz with the particle size about 0.01 mm,and the quartz content is more than 90%,as well as a small amount of clay minerals,dark metallic minerals and carbonate minerals.Among them,the red impurity minerals are distributed in the form of fine dots or dipping,with fine particle size(1-20μm);and the green impurity minerals are distributed in the form of flakes and fibres.The results of infrared transmission spectroscopy(potassium bromide tabletting method)showed that there are different degrees of molecular water in the void of the agate samples’microstructure.The red,purple,and colourless agate samples have basically no characteristic peak of structural water at 3628 cm^(-1);the green samples show a significant absorption peak at 3628 cm^(-1),and it is speculated that the structural water contained in the water-bearing minerals causes absorption here.Raman spectroscopy tests revealed a very s

关 键 词：紫绿玛瑙 石英 矿物组成 致色机理 

分 类 号：TS933.2[轻工技术与工程] P619.28[天文地球—矿床学]