Mineralogical and Gemmological Characteristics of "Sakura Agate"

Abstract

"Sakura agate" is a relatively new kind of agate in the domestic market. It has the characteristic "sakura-shape" inclusions and its common colour is colourless-pink series. The gemmological characteristics, mineral components, structure and the formation of different colours of "Sakura agate" were studied by hand specimens observation, polarizing microscoic observation, conventional gemmological tests, infrared spectrometer, micro-Raman spectrometer, electron probe, micro-area X-ray fluorescence analysis and EDS. The results showed that the main mineral components of the substrate and inclusions of "Sakura agate" are α-quartz while a small amount of moganite can be found in substrate. The substrate is cryptocrystalline quartz, while the inclusion is consist of crystalline quartz. The colour difference of "Sakura agate" is due to the different types and contents of trace elements. The pink-orange substrate is mainly caused by Mn and Fe elements, while the rare green inclusions are mainly caused by Fe elements. There are some gypsum and barite grains in inclusions, indicating that when the inclusions are formed, the ore-forming fluid is rich in barium (biological barium) and calcium, and there might be sulfate-containing pore water mixed in, resulting in the unstable mineralization conditions.