摘要
二轴晶矿物的３个主折光率分别为Ｎｇ、Ｎｍ和Ｎｐ．它们之间的关系如果是Ｎｇ－Ｎｍ＞Ｎｍ－Ｎｐ时，矿物为正光性；反之，则为负光性。即Ｎｍ＝１２（Ｎｇ＋Ｎｐ）为二轴晶矿物光性正、负的分界。然而，通过对这一判别式进行深入的分析发现，此判别式为一近似式，用这一标准进行二轴晶矿物光性判别将有一部分负光性矿物被误判为正光性。推导出了二轴晶光性的准确判别式，并用于对《透明矿物显微镜鉴定表》中所收录的７９０余种二轴晶正光性矿物进行了核查，结果发现有５４种矿物的光性被误判为正光性。
Three principal indexes of refraction of biaxial crystals are marked as N g, N m and N p respectively, with N g as the largest and N p the smallest. In optical mineralogy, the relative magnitude of ( N g- N m) and ( N m- N p) are often used to the discrimination of optically positive biaxial crystals from optically negative ones. If N g- N m> N m- N p, then the mineral is optically positive, otherwise it is optically negative. According to this standard, if N m=12( N g+ N p), the mineral should be optically neutral. A detailed study shows that this standard for discrimination of optical property of biaxial crystals is only an approximate one. If all the biaxial minerals were discriminated by using this standard, then a number of optically negative ones would have been wrongly labeled as optically positive. This paper derived an accurate equation for the discrimination of optical property of biaxial minerals on the basis of an imaginary indicatrix of optically neutral mineral, which is then used to check the minerals listed as optically positive ones in the book 《Identification of Transparent Minerals Using Microscope》 compiled by Institute of Geological Minerals of China Geoscience Academy, and 54 wrongly sorted minerals are detected.
出处
《石油大学学报（自然科学版）》
CSCD
1998年第5期11-13,25,共4页
Journal of the University of Petroleum,China(Edition of Natural Science)
关键词
矿物
二轴晶
正光性
负光性
mineral
biaxial crystal
optically positive
optically negative
