A Preliminary Study Of The Micro-fabric Features Of Jades Of SiO₂

Jades of SiO₂ are widely found and varied in the world,and also have more than 30 kinds of trade names,which make people bewilder when classify and select them.With the purpose of reasonably classifying Jades of SiO₂,clearly providing customers value orientation and strictly standardize market order,this dissertation observes various kinds of thin sections of Jades of SiO₂;concludes and categorizes their micro-fabric's features.Finally,a systematic and scientific plan of categorizing Jades of SiO₂ will be proposed.According to the degree of crystallization and crystal grain,the author divides Jades of SiO₂ into four categories:1)phanerocrystalline;2)microcrystalline-cryptocrystalline;3)cryptocrystalline-colloid;4)colloid.Then,the author observes and analyzes their features through microscope.Jade of SiO₂ in phanerocrystalline category generally own idiomorphic-hypidiomorphic granular textures,with average diameter of 0.10-0.50mm and longest diameter of 2mm.Its quartz crystal distributed directionally;the grain bound is well-defined and the crystal grain is wide-gapped.Under the crossed polarizers,Phanerocrystalline will display the features of four times dark and bright extinction.The typical jade of Phanerocrystalline is quartzite.Jade of SiO₂ in microcrystalline-cryptocrystalline class mostly consists of xenomorphic and granular quartz.The grains have good adhesion,which makes it difficult to distinguish the crystal grain.Microcrystalline-cryptocrystalline usually have a diameter of 0.01-0.03mm.Sometimes the diameter is less than 0.01m,and in this circumstance,people can not differentiate them through the microscope.Under the crossed polarizers,people can see“water cube”textures.The typical jade of this category is chalcedony.Majority of cryptocrystalline-colloid category are in radial-fibrous shape,while some of them have xenomorphic granular textures,which means geode may appear inside.Some fined grain's diameter is about 0.01-0.05mm;the grain has good adhesion and the grain bound is too dark to recognize.The radial-fibrous part is quartz of smaller grain in directional arrangement.Due to the diameter of grains is less than 0.01mm long,its crystal grain can not be distinguished under the microscope.The radial-fibrous-fine grained textures can grow in an interbedded way,leads to banded structure or concentric circle structure.In certain cases,“black cross pattern”extinction or“water cube”structure will appear.The typical jade is Agate.Jades of SiO₂ from colloid amorphous category possess a extremely subtle colloid structure.Under crossed polarizers,a total extinction will appear.This phenomena is almost the same as when it under monoscope.People can discover crystalline grain or play-of-color effect in some part of the jades.Observing the thin section,a plenty of spherical cross pattern extinction of colloid can be seen.The cross pattern extinction can move as the this section moves.The typical jade is Opal.The dissertation applies the micro-fabric features of Jades of SiO₂ to the classification of jades.Huanglong Jade has large crystal grains,with the diameter up to 0.05-0.10mm.It has idiomorphic-hypidiomorphic granular mosaic textures,like quartize.In other words,Huanglong Jade,falls into the phanerocrystalline category.However,Burma Huanglong Jade has xenomorphic granular textures,with crystal grain distributing averagely and adhering closely.The diameter of crystal grains is 0.02-0.05mm long.In the aspects of occurrence,grain size and grain adhesion,it has the similar features to chalcedony,so it should belong to microcrystalline-cryptocrystalline category.To some extent,Burma Huanglong Jade is yellow chalcedony.“Shuimozi”is a kind of Burma Huanglog Jade which can be widely seen in the market.The sample of“Shuimozi”shows that it mainly consist of quartz,and has SG:2.64,RI:1.54.The color is distributed averagely;the crystal grain has idiomorphic-hypidiomorphic granular mosaic textures;the diameter is 0.03-0.15mm long,which means it has the features of quartz.Therefore,“Shuimozi”is a member of phanerocrystalline category,that is Jades of quartzite.