The Study On Gemological Characteristics And Genesisof Nanhong Agate From Liangshan,Sichuan Province Of China

By the observation and test of orthogonal Polarization microscope,Scanning electron microscope,Cathodoluminescence,electronic probing analysis and Infrared Spectrum,Raman spectrum and Differential Thermal Analysis.The paper expects to make some explanation about the structure of“crystal core”structure and other related structure.The growth structure of the Nanhong agate is presented granular,short-fiber,long-fiber or alternating structure by the observation with Polarizing microscope.These structures are related to the exchange between hydrothermal and parent rock and the exchange of components between different body phases inside the agate.Combined with experimental data such as Infrared Spectroscopy,X-ray powder diffraction,Raman spectroscopy,it can be known that the main mineral in the Nanhong agate is?-quartz,and the chromogenic minerals are mainly hematite,and the traces at the white strip can be measured moganite,In addition,some samples can be observed with calcite under the Polarizing microscope.Combined with electron probing analysis,besides Si O2,there are Na?Mg?Al?F?K?Ca?P?Ba?Fe?Mn?Ti?Ni and other rare earth element.Trace element Fe was found in the red band,and the suspected barite mineral was found in the black rock area,and the content of rare earth element Ce was considerable.Combined with Cathodoluminescence experiments and electron,we can see that,overall,the fluorescence of Nanhong agate is not strong,and it may be related to the inhibition of Fe³⁺,while the red band emits weak red fluorescence,which may be related to the presence of inclusions containing Fe³⁺.Regarding the“crystal core”region and the white strip region,light blue fluorescence is emitted because Al³⁺partially replaces Si⁴⁺in the lattice and is also related to the content of Ti⁴⁺.Summarizes the previous analysis of the genesis of other types of agate structures and combines them with the experimental results to speculate the genesis of the Nanhong agate in Sichuan:During the process of chalcedony formation,it is speculated that the cryptocrystalline structure is formed in an unstable envirocm-1ent.Al,Ca,Fe,Na,K,and other elements enter the silica vein.The interaction between the volatile fluids of the parent rocks and magma and the high-temperature atmospheric water will help the formation of chalcedony.The inclusion of rich Fe can explain the formation of red color in Nanhong agate of Sichuan near the surrounding rock.Changes in the elemental content of the formation process(eg,Al,Na,Fe,etc.),as well as the periodic entrance of hematite and other symbiotic minerals,It results in the formation of bands in Nanhong agate in Sichuan.When the concentration of hydrothermal solution decreases and the number of crystal nucleuses decreases,the crystallization rate slows down.Increased solution temperature,reduced Si O2hydrothermal concentration,and water loss all contribute to the formation of a"crystal core"structure.