确定二轴晶宝石Nm值的实用作图法  

Application of the Graphing Method to Measure Nm Value of Crystal

作　　者：孟祥振[1] 赵梅芳[1] 郭昀[1] 

机构地区：[1]上海大学材料科学与工程学院,上海200444

出　　处：《上海地质》2010年第4期87-89,共3页

摘　　要：在宝石的日常鉴定工作中,二轴晶宝石的光性正负,都是根据主折射率Ng、Nm和Np值的相对大小判定的。在宝石折射仪上测出Ng和Np值相对较容易,而要测出Nm值则较困难。难点在于即使测到了Nm值,绝大多数情况下,测定者也是不知道的。因此必须通过作图求得Nm值。在二轴晶宝石的折射率中有Ng>Ng'>Nm>Np'>Np,每测得一大一小两个折射率值,其中有一个是Nm,或在大小两个折射率值之间包含了Nm的数值,这是作图求Nm值的科学依据。本文介绍的作图法简便、实用。The optical sign of biaxial crystal minerals is determined by relative values of major indices of refraction,i.e.Ng,Nm and Np during the identification of gemstone.The value of Nm is more difficult to be measured directly by using gemstone refractometer Than those of Ng and Np.In general the measurer does not know the actual value of Nm even if it is measured.It is well known that the values of indices of refraction are Ng﹥Ng′﹥Nm﹥ Np′﹥Np,and the Nm values vary between the other two indices of Ng and Np or Ng′and Np′.According to the relative values of these indices of refraction,a simple and practical graphing method was developed in this study to measure the Nm value.

关 键 词：二轴晶宝石 光性正负 主折射率 作图求Nm值 

分 类 号：P619.281[天文地球—矿床学]