Mineralogical Characteristics of“Jinsiyu”(Quartz)

A kind of marron jade with its commercial name"Jinsiyu"was newly found in Xinjiang.A sample was collected and mineralogical characteristics and coloration of the sample were investigated by X-ray diffraction,X-ray fluorescence,scanning electron microscope and ultraviolet-visible spectrophotometer.This maroon and translucent jade has a typical glass luster. Under transmission light,some tiny filaments are observed distinctly in irregular arrangement, Conventional gemmological test results show that the refractive index of the jade is 1.54 (point measurement) and the specific gravity is 2.64 and the hardness is bigger than that of a steel knife. Accordingly.the main mineral component of sample is preliminarily inferred to be quartz.The patterns of X-ray diffraction show the sample has peaks at 4.25 Å(100), 3.33 Å(101).2.45 Å(110),2.28 Å(102), 2.23 Å(111), 2.12 Å(200), 1.98 Å(201) and so on, It reveals that the main mineral component of the sample is quartz.The result of X-ray fluorescence demonstrates that the main chemical composition of the sample is Si. It also contains a small quantity of Al and trace amount of Fe, Mg, K, Mn, Na, Ti and P.Scanning electron microscope result shows that angular quartz particles constitute the sample. Most of the quartz particles is bigger than 5 microns, and some smaller than 2 microns. The result of the energy dispersive spectrometer tells that the sample contains trace amount of C. Surface scanning analysis shows that evenly dispersing Fe leads to the maroon tone.The coloration theory was studied by using ultraviolet-visible spectrophotometer. The diffuse reflection spectrum reveals that the existence of Fe in the sample is mainly in two forms:hematite and goethite. It is because the combination of the two coloration minerals that leads to the maroon colour of the sample. In addition, the high content of hematite is the main reason of the partial red colour.