中文摘要：

为了查明埋藏3000-5000a的三星堆和金沙出土古象牙珍贵文物的损害机理，为实施有效保护提供科学依据，采用X射线衍射对比分析了古象牙物相和结晶特征及其与新鲜亚洲象牙的差别。结果表明：金沙和三星堆古象牙和新鲜象牙的主要物相是结晶度较差的碳羟磷灰石。由于古象牙的衍射峰比新鲜象牙的分裂更为明显、尖锐，且（002）衍射峰半高宽值比新鲜象牙的小，说明虽经几千年地下埋藏，古象牙中碳羟磷灰石晶体结构不仅没有破坏，而且结晶度还有所提高。古象牙与新鲜象牙的最大区别在于，在象牙材料中主要起粘结相作用的有机成分已受到侵蚀和破坏，这可能是古象牙出土脱水后容易粉化破坏的主要原因之一。

英文摘要：

In order to find out the mechanism of decay of ancient ivory unearthed from Jinsha of Chengdu and Sanxingdui of Guanghan, China, which had been buried for 3 000 to 5 000 years, and provide the scientific basis for an effective method to protect them, the main phases and crystalline characteristics of ancient ivory and the difference between ancient and fresh ivory were analyzed and contrasted by X-ray diffraction. The results show that the main phase of ancient ivory is poor crystalline carbonate-hydroxyl-apatite. The diffraction peaks of ancient ivory are more distinct and speculate than that of the fresh ivory, and the full width at half maximum of the （002） peak of the ancient ivory is less than that of the fresh ivory. These results show that the crystallinity of the ancient ivory is higher although it has been buried for several thousand years. The big difference between the ancient ivory and the fresh ivory is that the organic composition, which plays an essential role as cohesion phase in the structure of the materials, had been eroded and destroyed. This may have been one of the reasons that ancient ivory is easily dehydrated and pulverized after it has been unearthed.