大化墨玉的矿物学特征

Mineralogical characteristics of Dahua dark nephrite,Guangxi

一种新的墨玉最近在广西大化瑶族自治县被发现。对该玉石的宝石学、岩石学、矿物学特征的系统研究表明,其质地细腻,主要组成矿物有阳起石和铁阳起石(95%以上),呈显微毛毡状、柱状结构,含特征次要矿物黑硬绿泥石,并常含黄铁矿、磁黄铁矿。作为一种新型的墨玉成因矿床,大化墨玉产于辉绿岩与围岩碳酸盐岩的内接触带,是夕卡岩化后热液交代作用的产物。与其他产地墨玉相比,宝石学特征基本相同,但大化墨玉成分上更富铁,主要由铁含量高的矿物组成,密度略偏高。其黑色是由高铁含量的阳起石-铁阳起石所致。

A new kind of black nephrite was found in Dahua Yao Autonomous County,Guangxi Zhuang Autonomous Region.In this paper,gemological,petrological and mineralogical characteristics of the nephrite were studied.The results show that the fine and moist nephrites with micro-interwoven fibers and micro-prismatic textures are composed mainly of actinolite and ferroactinolite,and contain typical minor mineral stilpnomelane together with pyrite and pyrrhotite.As a new genetic type of dark nephrite deposit,the Dahua black nephrites occur in the inner contact zone between diabase and surrounding carbonate rocks and were formed by hydrothermal metasomatism after skarnization.The Dahua black nephrites have almost the same gemological characteristics as the black nephrites from other places,whereas the Dahua black nephrites with slightly higher density are iron-richer in composition and consist mainly of minerals with high iron content.The color of Dahua black nephrites is caused by actinolite-ferroactinolite with high iron content.