甘肃马衔山软玉的宝石矿物学特征
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摘要
甘肃省临洮县马衔山存在软玉矿脉。对绿色、黄绿色、黄褐色的马衔山软玉样品进行了常规宝石学、红外光谱、电子探针、扫描电镜测试及偏光显微镜观察。结果表明,样品的点测折射率为1.61,密度为2.917～2.941 g/cm~3(不含风化层),摩式硬度为6～6.5,具油脂光泽,韧度很高,主要组成矿物为透闪石(w(SiO_2)=57.06%～58.44%、w(MgO)=23.42%～24.13%、w(CaO)=12.24%～13.04%),次要矿物为透辉石、绿帘石、磷灰石、榍石、斜黝帘石等,主要为显微纤维变晶结构或毛毡状变晶结构,各项特征均符合软玉的国家鉴定标准,同时推测样品的绿色深浅与Fe含量有关。此外,样品常存在白色风化层,内有沿裂隙分布的褐色树枝状物质(俗称"蚂蚁脚"或"藻丝纹"),在白色风化层和玉质部分间常出现褐色过渡层。
There are veins of nephrite in the Maxianshan area, Lintao County, Gansu Province. In this paper, the green,yellowish green and brown colored nephrite samples were investigated using the conventional gemological method,infrared spectroscopy, electron probe, scanning electron microscope, and polarizing light microscopy. The results show that the nephrite samples have the spotty measured refractive indexes of 1.61, densities of 2.917-2.941 g/cm~3( not including the weathered layer), Mohs hardnesses of 6-6.5, with greasy luster and high toughness. The nephrite samples contain essential mineral of tremolite(w(SiO_2)=57.06%-58.44%, w(MgO)=23.42%-24.13%, w(CaO)=12.24%-13.04%), and auxiliary minerals of diopside, epidote, apatite, sphene, and clinozoisite, with major micro-fiber crystalloblastic or felt-like crystalloblastic textures. All these characteristics are consistent with those of the China national standard of nephrite. It is believed that the green color intensities of samples could be related to the Fe contents. In addition, there are white weathered layers with brown dendritic substances(with nickname of "ant feet" or "algae stripes")distributed along fissures in nephrite, and brown transition layers between the white weathered layer and nephrite body.
There are veins of nephrite in the Maxianshan area, Lintao County, Gansu Province. In this paper, the green,yellowish green and brown colored nephrite samples were investigated using the conventional gemological method,infrared spectroscopy, electron probe, scanning electron microscope, and polarizing light microscopy. The results show that the nephrite samples have the spotty measured refractive indexes of 1.61, densities of 2.917-2.941 g/cm~3( not including the weathered layer), Mohs hardnesses of 6-6.5, with greasy luster and high toughness. The nephrite samples contain essential mineral of tremolite(w(SiO_2)=57.06%-58.44%, w(MgO)=23.42%-24.13%, w(CaO)=12.24%-13.04%), and auxiliary minerals of diopside, epidote, apatite, sphene, and clinozoisite, with major micro-fiber crystalloblastic or felt-like crystalloblastic textures. All these characteristics are consistent with those of the China national standard of nephrite. It is believed that the green color intensities of samples could be related to the Fe contents. In addition, there are white weathered layers with brown dendritic substances(with nickname of "ant feet" or "algae stripes")distributed along fissures in nephrite, and brown transition layers between the white weathered layer and nephrite body.
引文
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[2]张晓彤,金晓明.甘肃史前玉器探析[J].丝绸之路,2011,10:26-28.
[3]丁哲.“甘肃玉”之我见[J].丝绸之路,2015,15:75.
[4]GB/T 16553-2017,珠宝玉石鉴定[S].
[5]郭立鹤,韩景仪.和田玉、玛纳斯碧玉和岫岩老玉中M1、M3阳离子占位的红外光谱分析[J].岩石矿物学杂志,2002(S1):68-71.
[6]史淼.新疆和田碧玉的矿物学特征及成因初探[D].北京:中国地质大学(硕士论文),2012:25-26.
[7]张永旺,刘琰,刘涛涛,等.新疆和田透闪石软玉的振动光谱[J].光谱学与光谱分析,2012(2):398-401.
[8]彭文世,刘高魁.矿物红外光谱图集[M].北京:科学出版社,1982:363.
[9]廖任庆,朱勤文.中国各产地软玉的化学成分分析[J].宝石和宝石学杂志,2005(1):25-30.
[10]吴之瑛,王时麒,凌潇潇.辽宁岫岩县桑皮峪透闪石玉的玉石学特征与成因研究[J].岩石矿物学杂志,2014,33(S2):15-24.
[11]张勇.新疆和田玉的宝石学特征研究[D].北京:中国地质大学(硕士论文),2011:41.
[12]杜季明.广西大化透闪石玉的宝石矿物学特征研究[D].北京:中国地质大学(硕士论文),2015:56.
[13]赵文俞,牟善斌,秦麟卿,等.木兰山蓝片岩中斜黝帘石-低铁绿帘石连生体的确定[J].岩矿测试,2002(1):29-32.