Host-rock characteristics and geochemistry of the Rongkong Opal-C Mineraloid, North Luwu Regency, South Sulawesi Province, Indonesia

Opal can be found in several locations, including America, Tanzania, Brazil, Mexico, East Africa, Indonesia and Australia, which is now the world's top producer of black opal. One of the most economically valuable gems in the world is the mineraloid opal. In the Rongkong area, opal is found in the host rock of volcanic igneous rock, namely andesite. This study aims to determine the opal mineraloid host-rock's microstructural characteristics and the elemental and compound content of the opal mineraloid host-rock's geochemistry in the Rongkong area, Indonesia. The research took three samples in the field as large as hand specimens. The three samples were one host -rock sample and two opal mineraloid samples; the samples were then prepared and analyzed in the laboratory. Laboratory analysis was performed using SEM -EDS, XRF and petrographic analyses. The results of the SEM -EDS test analysis showed that most opal mineraloid carrier rock constituents are aluminum and oxide. This can be seen from the substantial Al and O content. In samples 1 and 2, Al, O, Ca and P with the highest composition of chemical compounds are Al2O3, CaO, and P2O5. The Rongkong opal mineraloid from Limbong Village, Rongkong District, North Luwu Regency, South Sulawesi, based on the results of XRF analysis, contains the chemical compounds SiO2, Al2O3, K2O, Fe2O3, CaO, TiO2, RuO2, SrO, MnO, V2O5, Rb2O, Ag2O and CuO. The content compound that is more dominant in opal mineraloids is SiO2 due to silicate enrichment in the forming of opal mineraloids.