明溪石榴石的宝石学特征

产于福建明溪的石榴石有两种类型 .一种为紫红色 ,具有主波长 5 85～ 5 88nm ,饱和度 0 .5 6 9～ 0 .6 2 9,折射率 1.74,密度 3.6 5～ 3.78g/cm3;另一种为褐红色 ,主波长 5 95～ 6 0 0nm ,饱和度 0 .86 6～ 0 .939,折射率1.75～ 1.76 ,密度 >3.8g/cm3.在RI -D图上 ,前者属镁铝榴石 ,而褐红色的石榴石落在铁铝榴石—镁铝榴石区域内 .明溪石榴石含有特征的钉状包裹体 .电子探针分析表明 ,紫红色的石榴石中含有较高的Cr,而褐红色的石榴石中则富含Fe和Ti.文章还探讨了明溪石榴石的吸收光谱特点及颜色成因 .

The gemological features of the garnets from Mingxi, Fujian

There are two types of garnets found in Mingxi gemstone deposit, Fujian Province. One is purplish-red in color, with the main wavelength of 585-588?nm and saturation 0.569-0.629 in their chromatic measurement, the other is brownish- red, with the main wavelength of 600-595?nm and saturation 0.866-0.939. The purplish-red garnet has the refractive index of 1.74, the density of 3.65-3.78?g/cm\+3 and the brownish-red garnet is 1.75-1.76 in RI and over 3.8?g/cm\+3 in density. In the RI-D diagram of Webster(1983), the purplish-red one falls into the category of pyrope and most of the brownish-red garnet almandine-pyrope. The conclusion is conformed by microprobe analysis, which also shows that the purplish-red type is higher in Cr while the brownish-red garnet is richer in Fe and Ti. In the optional absorption spectra of the Mingxi garnets, the purplish-red type has absorption at 410 and 570 nm, which have been assigned into Cr 3+ in the crystals and the brownish-red type shows the broad band from 590-400nm which peaks at 410 and 510?nm.