Study On The Difference Of Heat Treatment And Spectral Characteristics Of Different Agate Varieties

In this paper,seven agate varieties,Liangshan Nanhong agate,Baoshan Nanhong agate,Brazilian agate,Madagascar agate,North Red agate,Xuanhua Warring States red agate and Datong agate,were experimented on.The varieties were classified and heat-treated,and modern testing techniques such as differential thermal analysis,gemstone microscope,scanning electron microscopy,infrared spectroscopy,Raman spectroscopy and optical fiber spectroscopy were used.Various properties of agate before and after heating were analyzed in detail.Through magnifying observation and microscopic observation,a series of color and structure changes occurred in agate during the heat treatment.With the increase of temperature,gray color appeared in all samples.When the Datong agate is heated to 500?,the purple fades completely while when the other agates are heated to600?⁷00?the color begins to fade and whiten.At the same time,scanning electron microscopy?SEM?showed that a large number of micro-cracks appeared in all agate cultivars when heated above 500?.Differential thermal analysis showed that the water content in agate ranged from0.2%to 2.2%.Adsorbed water was released from room temperature to 200?during heat treatment and structured water was released from above 600?.When the structural water escapes,the agate structure is destroyed,the transparency becomes low and the cracks increase.According to optical fiber spectrum analysis,it is unreliable to improve the color of agate by heat treatment alone.It can not only change the color of agate?heating non-red agate to red agate?or greatly improve the color of red agate but also reduce the brightness of agate and make the agate show a darker tone.According to infrared spectrum analysis,the absorption peaks of all agate varieties are mainly quartz and there is no obvious difference in infrared spectrum data before and after the heat treatment.The relative content of clinoptilolite was calculated by using the method of calibrating the relative content of clinoptilolite with the value of I₁₀₉₅/I₁₀₅₇ in infrared spectroscopy.It was found that the content of clinoptilolite decreased with the increase of the annealing temperature of agate.According to Raman spectroscopy analysis,goethite is found in most agate and goethite will lose water to hematite with the increase of heat treatment temperature.At the same time,501cm^-1 peak is the characteristic peak of plagiosilica.The relative content of plagiosilica can be calculated by the integral ratio of the two peaks at 464cm^-1 and 501cm^-1 of Lorentz fitting curve.The agate varieties containing plagiosilica can reduce the content of plagiosilica by heating.This is consistent with the experimental data of infrared spectroscopy.