缅甸翡翠中“Cr的淡化”及意义

Desalinization of Chromium within Myanmar Jadeite Jade and Implications

认为缅甸翡翠在形成的过程中存在“Cr的淡化”现象,探讨了该现象在翡翠绿色形成和演化过程中的表现形式及意义。缅甸翡翠中“Cr的淡化”可划分为4个阶段:(1)铬铁矿→钠铬辉石,该阶段是交代反应,形成冠状和柱粒状结构;(2)钠铬辉石→铬硬玉,该阶段是交代—置换反应;(3)铬硬玉→含Cr低的硬玉[w(Cr2O3)约为0.3%],该阶段是重结晶置换反应;(4)含Cr硬玉进一步淡化,本质上该阶段是第三阶段的延续。缅甸翡翠中“Cr的淡化”受相邻矿物种类、剪切应力所致的后期变质变形机制和强度以及p/t条件和流体等因素的影响。在缅甸翡翠中,“Cr的淡化”贯穿翡翠形成过程的始终。用“Cr的淡化”能很好地解释缅甸翡翠绿色具独特色形、颜色浓淡变化大等特征,对于认识翡翠绿色及其变化、解析以及评价翡翠原石等具有重要意义。

This paper presents a new viewpoint that there exists the desalinization of chromium within the Myanmar jadeite jade, which plays an important role in genesis and evolution of green colour of the jadeite jade. The desalinization of chromium within the Myanmar jadeite jade is divided into four stages： （1） transformation from chromite to kosmochlor, which is characterized by the metasomatic reaction, forming corona texture or granoblastic texture; （2） from kosmochlor to chromian jadeite, which is regarded as the replacement reaction, accompanied by metasomatism; （3） from chromian jadeite to low chromium-bearing jadeite [w（Cr2O3）=±0.3%], which is the replacement reaction accompanied by recrystallization induced by deformation, and （4） from chromium-bearing jadeite to lower chromium-bearing jadeite, which is essentially the further evolution of the stage 3. The desalinization of chromium within the Myanmar jadeite jade is influenced by variety of neighbor minerals, the way and intensity of deformation/metamorphism induced by shear stress, p/t condition and fluids. Using the desalinization of chromium, the feature that green colour in jadeite jade has special shape can be interpreted, and how and what the green colour changes can be understood.