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本文研究了河北省涉县符山铁矿夕卡岩中石榴石的双折射性。该石榴石属钙铝-钙铁榴石系列,有较强的双折射性,重折率最大值约为0.009。加热可使双折射性减弱甚至消失。依形成温度,可将石榴石分为两群,重折射率相差一、两个数量级,形成温度较低者其双折射性强。在每一群中,重折率与分子式中八面体位置 Al 含量成上弯曲线关系,最强双折射大致在 And_(65) Gro_(35)成分处。X 光单晶衍射照相出现异常,衍射点变成由数个点组成的拉长的线,这些点沿一定方向排列,强度和数目有变化,可能是因为结构中八面体位置上 Fe~(3+)/Al 有序引起的。有序引起石榴石对称性降低,变为二轴晶,可以较好地解释石榴石双折射性的成因及其变化规律。本文还讨论了环带与双折射性的关系。
In this paper, the birefringence of garnet in skarn from Fushan Iron Mine, Shexian County, Hebei Province was studied. The garnet is a series of Ca-Al-Mg-Fe garnets with strong birefringence and the maximum value of birefringence is about 0.009. Heating can reduce or even birefringence disappear. According to the formation of temperature, garnets can be divided into two groups, the refractive index difference of one or two orders of magnitude, the formation of the lower temperature birefringence and strong. In each group, the birefringence has a curved relationship with the octahedral Al content in the molecular formula, and the strongest birefringence is roughly at the And_ (65) Gro_ (35) component. X-ray single crystal diffraction photography abnormalities, the diffraction point into several points by the elongated line, these points along a certain direction, the intensity and the number of changes may be due to octahedral structure of the structure of Fe ~ (3 +) / Al orderly caused. Orderly cause the symmetry of garnet reduced to become two-axis crystal, which can better explain the birefringence of garnet causes and its variation. The paper also discusses the relationship between annulus and birefringence.