Geographic origin determination of peridot using defect types and chemical characteristics

Abstract

Peridot, the gemological term of olivine, has been one of the most commercially important gemstones throughout history. Gem-quality olivine is classified into three types based on geological genesis: basalt-related (igneous) type, metamorphic/hydrothermal type and extraterrestrial origin. We compared FTIR spectra and trace element chemistry of peridot samples from various sources including Burma, Pakistan, Egypt and Norway to distinguish them. Hydroxyl in olivine can be detected as absorption bands in FTIR spectra and is considered to be associated with defects within olivine structure. The types of defect are related to the geological origin of peridot and classification of defect types using FTIR can be helpful to distinguish them. In addition, chemical analysis using several key elements such as Mg, Ni, Fe and B are helpful to separate peridots from various sources. FTIR and trace element chemistry can be used to determine geographic origin of metamorphic/hydrothermal peridot. On the other hand, determining origin of basalt-related peridot is challenging for now because they show similar defect types and overlapping chemistry.