Research On Gemological,Mineralogical And Microstructural Characteristics Of Beaded Freshwater Cultured Pearls From Zhuji,Zhejiang Province

Beaded Freshwater Cultured Pearls?FWCPs?from Zhuji,Zhejiang Province is mainly characterized by big size,variable color and strong luster.In this paper,the author discusses the the gemological characteristics,chemical compositions,mineral phases,spectroscopy characteristics,and color-causing of 31 Beaded FWCPs,compared with 5 Non-beaded FWCPs,which are all from Zhuji,Zhejiang Province.This paper focuses on the structure of beaded FWCPs.The study is done by using Gem Microscopy,Polarized Microscopy,FE-SEM,FITR,Micro-IR,Raman Spectrum,Cathode Luminescence,Ultra-visible Spectrum,Differential Thermal Analysis.The results as follows:The main components of FWCPs are CaCO₃,organics and H₂O.CaCO₃ exists in aragonite phase,accidentally in vaterite.The vaterite distributes around the bead,the clearance between layers and around the hole.In CL,the bead and the layer of aragonite show green fluorescence,while the vaterite shows orange.Also the brightness of nacre's CL fluorescence is different.The deeper layers under Polarized Microscopy show brighter green fluorescence.The FITR shows 696.3?711.7?877.6?1085?1479.3¹492.8cm^-1 of aragonite.The Raman Spectrum shows 1089?705?280?271?215?191?153?144cm^-11 of aragonite.The Carotene,the Raman peaks of which are 1131?1525?1005.7¹023.8and 1295 cm^-1,is considered to impact the main body color of yellow and pink FWCPs.There is no 1005.7¹023.8 and 1295 cm^-1 peaks in the Raman Spectrum of the purple pearls.The color of purple pearls is related to the polyacetylene.By Polarized Microscopy observation,the beaded FWCPs include a bead,organic layer,prismatic layer and aragonite layer.The prismatic layer has many forms of existence,such as elongated needle,columnar,burr and“nail-head”.The pictures of SEM show that the prismatic layer is generally made of cylindrical or banded aragonite fibers.It was the first time that the prismatic layer was found in completely natural-crystal morphology,existing near the bead or around the hole.Most of the fibers are oriented nearly perpendicular to the aragonite sheet.The fibers are arranged in parallel to the aragonite sheet or radial direction were observed in this study.The aragonite platelets form in hexagon,pentagon,heptagon and other similar shapes.The thickness of aragonite platelet decreased from the center of the pearl to the surface.