产自西藏丁青县的“象牙玉”结构致密, 适于雕刻, 绝大多数玉石呈白色, 有的部位分布有红色细脉。 采用常规宝石学仪器、 扫描电子显微镜(SEM)、 X射线粉晶衍射(XRD)、 傅里叶变换红外光谱(FTIR)和拉曼光谱(Raman)等测试方法对象牙玉进行了矿物学及谱学特征测试与研究。 常规宝石学测试结果表明, 象牙玉的相对密度为2.72~2.94, 折射率为1.68（点测）, 在长波紫外光下呈强白色荧光。 偏光显微镜下可见菱镁矿因为粒度极小而不具消光特征, 石英呈脉状穿插菱镁矿, 赤铁矿在菱镁矿裂隙中充填。 背散射电子像表明绝大多数基质为菱镁矿与石英的微晶混合物, 有的部位为较大石英颗粒（约25 μm）散布在菱镁矿中, 石英与赤铁矿呈微晶充填在菱镁矿的裂隙中。 X射线粉晶衍射中具有3.34和4.25 石英的特征衍射峰, 2.74, 2.10和1.70 菱镁矿的特征衍射峰。 在红外光谱中, 886, 1453和748 cm-1为碳酸盐矿物的特征吸收峰, 其中ν4（面内弯曲振动）的频率与阳离子半径的变化成正比, 因此748 cm-1指示其为菱镁矿; 1 089, 1 165, 798, 779, 694, 515和465 cm-1为石英的特征吸收峰。 根据拉曼光谱可知, 白色基质为菱镁矿与石英的混合, 透明脉状矿物为石英, 其中石英的拉曼图谱中还存在斜硅石的特征拉曼峰（500 cm-1）, 在以α-石英为主的石英质玉石中, 斜硅石的含量越高, 其结晶程度越低, I500/I465的比值与结晶程度成反比, 因此在菱镁矿中混杂的石英结晶程度比石英脉中的低, 两处均为隐晶质石英; 红色矿物具有1317, 655, 608, 492, 460, 406, 292, 242和222 cm-1的赤铁矿典型拉曼峰。 由于其原石并不存在生物迹象, 所以其成因与生物无关, 由于象牙玉为含隐晶质石英的泥晶质菱镁矿, 所以推测其成因与超基性岩的风化淋滤作用有关。

There is a new kind of magnesite jade which is white mostly and some part of it present red color in veins named ivory jade from Tibet. The structure is compact,and color is attractive.Thus it is an ideal stone to carve. The mineralogical and spectroscopic characteristics of the ivory jade are studied with the help of conventional gemological instruments, slice observation, scanning electron microscopy, X-ray powder diffraction (XRD), infrared spectroscopy (IR) and Raman spectroscopy. The gemological testing results show that specific gravity of ivory jade are 2.72~2.94, and reflection index is 1.68 (distant vision technique), strong white fluorescent light is observed under the ultraviolet lamp. There have not extinction characteristics of magnesite exists under the cross-polarized microscope, due to its granularity is too tiny. Quartz vein interpenetrates magnesite and magnesite cracks are filled by hematite. Backscattered electron imaging shows that thematrix is made of magnesite and microcrystalline quartz. There is also some larger size quartz (approximated 25 μm) spread in magnesite. Quartz and hematite are filled in cracks of magnesite as microcrystal. And few calcites are founded in magnesite. XRD testing confirms 3.34 and 4.25  which are characteristic diffraction peaks of quartz and 2.74, 2.10 and 1.70  are characteristics diffraction peaks of magnesite. The FTIR spectrum present 886, 1 453 and 748 cm-1 which are attribute to carbonate minerals characteristics absorb peaks and the frequency of ν4（in-plane bending vibration）is inversely proportional to the radius of positive ion, therefore, 748 cm-1 indicated the sample is magnesite; 1 089, 1 165, 798, 779, 694, 515 and 465 cm-1 are distinct peaks of quartz. According to Raman results, the white matrix is the mixture of magnesite and quartz. Transparency vein mineral is made of quartz. In the Raman spectrum of quartz, there are Raman shift 500 cm-1 which attribute to moganite. In group minerals of quartzite jade, as the main component mineral is α-quartz, if it were contained a great amount of moganite, it should find low crystalline. In another way, the value of I500/I465 is inversely proportional to crystalline. Thus, both are cryptocrystalline quartz and crystalline in magnesite is lower than in the quartz vein. 1 317, 655, 608, 492, 460, 406, 292, 242 and 222 cm-1 are attributes to Raman shift of hematite. Because there are no biological indication exists, its cause of formation is not related to biogenic. Speculating it may be formed related to weathering-leaching react to ultrabasic.