Study On Mineralogy And Criteria Of Quality Evaluation Of Dushan Jade

In this paper, the mineral components, characteristics of rock and precious stones and characteristics of the craft of Dushan jade from Nanyang area of Henan province were studied by integrated use of the theory and method in mineralogy, petrology and gemology, deposit geology, and geochemistry. Considering many features of Dushan jade, such as the color, variety, the degree of perfection, the new and old pit, the weight of block, mining and the consumption trends in market, the standard of evaluation the quality of Dushan jade was constituted.Dushan jade belonging to the silicate mineral rocks, is an altered-plagioclase or zoisite-altered plagioclase. It is mainly made up of 50%-90% of basic plagioclase (anorthite), 5%-70% of zoisite,5%-15% of chrome mica, 1%-5% of albite,1%-5% of epidote and 1% actinolite, and the biotite and tourmaline were less than 1%.There are some trace minerals, such as sphene, rutile, chromite, pyrite, and so on. Besides, the jade also comprises several secondary minerals, such as zeolite, grapes and calcite, limonite, sericite and chlorite. The minerals are different according to the type of jade.The physics character of Dushan jade is glass-oil sheen and fine texture, compact and hard, the hardness of 6.5-8 and cryptocrystalline .and the jade has complex color, granule texture and massive structure.The Dushan jade is identified form the color, granular structure, the degree of transparency and hardness, density and refractive index. It is distinguished the other similar jade (greenstone, jadeite and others) as high Al₂O₃, high calcium and high Sr.The source rock of Dushan jade is plagioclase which is formed in the process of crystallization and differentiation of magma. The forming process of Dushan jade is late dynamic metamorphism and hydrothermal metasomatism.The principles of quality evaluation of Dushan jade is the color, texture, perfect, blocks, the degree of scarcity, and the first three factors are the key conditions.The criteria of quality evaluation of Dushan jade are based on the color (including subspecies).The color of Dushan Jade may be divided into eight categories and 24 sub- categories and more than 10 mixed color and transitional color. So there are main types of Dushan jade in core, such as white-blue, full-green, lotus-red and lily-white.The criteria of quality evaluation of Dushan jade must be also considered the factors including degree of perfection, from new or old pit, weight of block and so on.