Study On The Color And Genesis Of Zhanguohong Agate From Fuxin, Liaoning Province

Zhanguo-hong agate is a kind of agate decorated with red,yellow or white bands,outputting in rhyolite near Cunzhuyingzi, near Beipiao district, Liaoning Province.Dozens of samples from the deposits have been chosen, and their components,characters of color and genesis have been studied in this thesis, experimentsincluding observation under microscope, XRD, electron microprobe analysis, SEM,CL, TGA etc. The appraisal standard of Zhanguohong agate is also discussed as wellas the identification points between several kinds of agate from different deposits.Comparing with other kinds of agate, the gemological characters of Zhanguohongagate is quite common with similar RI and SG. The texture can be seen under themicroscope in thin film and divided into four kinds: tiny grains, short fibre, longfibre and macrocrystalline quartz, repeat of these four kinds can be observed. SEMphotos show all these textures except macrocrysatlline are consist of tiny globulitesand small holes between them, but no fibre is found.Zhanguohong agate is mainly consist of α-quartz together with little moganite andwater under1%, and mogantie can be found in almost every sample. WhileMicro-Raman spectroscopy (short-range order) proved to be the perfect tool fordetecting the presence of moganite, the strongest band is located around501cm-1which can be distinguished from the464cm-1of quartz, these two peaks has beenused for the evaluation of the quartz/moganite ratio in agate samples. In areas withtiny grains and short fibre texture where the moganite is founded, this ratio can varysignificantly across a single specimen, which is between none to around20wt%,thus knowing the content of moganite in the overall agate can reach up to40%.The color patterns of Zhanguohong agate, such as bands, is formed by mass oftiny red or yellow dots which can only be seen under microscope and its color iscaused by Fe. And the minerals of these dots are goethite or hematite or the both,different ratio of geothite or hematite and SiO2can produce yellow or red colorwhile pure hematite can produce dark red and probably it is formed in the dehydrateprocess of goethite.By analysis former and this work, concluding that Zhanguohong agate mayformed in a solution rich in silica with low PH and the formation of bands is theresults of a sequence of sedimentation phases from the solution under the changes ofthe environment and the contents of the solution. Take the first time solution filledthe opening in the rock as the first phase of the sedimentation and the first phase can be divided into four stages: tiny SiO2grains crystallization, short fibre growth, longfibre growth and macrocrystalline quartz crystallization. The first phase ofsedimentation can be disturbed by the new solution coming in and the last twostages will repeat until the opening in the rock is filled with agate or no moresolution coming in, thus explaining the bands repeated in the middle of quartz.