Aspectos gemológicos de ametistas de Quixeramobim, Brasil

Abstract

Since the end of the 20th century, it has become extremely usual for countries with a remarkable exploration of gems to catalog and disseminate the properties of their gems for various purposes, such as market, academic or criminal. In Brazil, there is a gap in this regard; many mineral occurrences do not have their gemological properties tabulated or disclosed. Globally, gemological studies do not cease and gemological data on minerals are updated frequently; as in the case of tourmalines. In addition, the properties of minerals used as gems can help or even reveal new aspects about the geological evolution of the region where a mineral occurs. For the gemological characterization of amethysts from Quixeramobim (CE), the usual gemology equipment was used, such as: refractometer, dicroscope, spectroscope, polariscope, hydrostatic balance, fluorescent lamp and gemological microscope. Quixeramobim amethysts have the standard characteristics of amethysts from different parts of the world, but the abundance of oriented fluid and solid inclusions requires further study. With the exception of this peculiarity, amethysts have no anomalies; unlike the amethysts from Santa Quitéria, also from the State of Ceará, which have a very high birefringence as an anomalous characteristic. This demonstrates the importance of gemological characterization not only at a State / Regional level, but also at the Municipal scale, as in the same State there may be occurrences of the same mineral, but with divergent properties. Therefore, it is important to characterize the occurrences in different geological contexts, as the formation environment can interfere with the characteristics of minerals.