Gemological Characteristic Of Zhanguo Red Agate From Xuanhua District, Hebei Province

Zhanguo Red Agate from Xuanhua District, Hebei Province, was a characteristic agate discovered in recent years. It’s a relatively more recent discovery than Beipiao district, Liaoning Province. So there are few researches about this “new arrival”. In this paper, Zhanguo Red Agate from Xuanhua District, Hebei Province, is tested to study its gemological characteristics through a variety of conventional gemological instruments and modern methods including polarzing microscope, EMPA, XRD, IR spectrum, UV-Vis-Infrared Spectrum, Laser Raman Spectrum Analysis and CL, etc.Andesite is the surrounding rock of Zhanguo Red Agate from Xuanhua District. It’s has a typical porphyritic texture with vesicular structure and amygdala structure. The output of the agates aways have a shape as Spherical, reniform and concretion forms. And quartz or calcite often crystallized in the center. Zhanguo Red Agate has cryptocrystalline structure which is decorated with red,yellow black or white bands, while purple bands is relatively uncommon. It has vitreous luster, translucent – opaque. The basic gemological properties is similar to other agate. While the beautiful bands is unique.Polarzing microscope is used to find out that Zhanguo Red Agate is mainly composed of quartz, with cryptocrystalline, granular, short fibrous and long fibrous structure. Previous studies used scanning and transmission electronic microscope studies have revealed that virtual fibers are composed of even smaller, slightly elongated crystallites(8-100 nm, invisible in optical microscopy) that are aligned on a much finer scale parallel to the orientation of the virtual fibers. The color patterns of Zhanguo Red Agate, such as bands, is formed by mass of tiny red or yellow dots which can only be seen under microscope and its color is caused by iron oxide or iron hydroxide. And Laser Raman Spectrum Analysis proved that the minerals of these dots are hematite or goethite or the both.Zhanguo Red Agate is mainly consists of α-quartz together with little water under 1%, and the crystallinity of quartz is low. First derivative of the UV-Vis-Infrared Spectrum is quoted in agate for the first time, and then come to a conclusion that hematite causes red color and goethite yellow. Under the effect of cathode electron, hematite and goethite present dark red color due to containing Fe3+, black point present not light because containing Fe2+.