Characteristics And Genesis Of Precious Opal-Ct From Banten, Java, Indonesia

Precious gemstone especially black opal with charm and beauty play of colors was found at Lebak Regency, Province of Banten, situated in the western part of Java Island, Indonesia. The opal is hosted by grayish claystone member of early Pliocene Genteng Formation, consisting of volcaniclastics, rich of volcanic glass as fluvial sediment. The host rock of opal is overlain by polymictic conglomerate or pebbly sandstone representing river sediment. The Banten Opal spread over a limb of anticline with east – west direction, at Tuff unit sediment, with more than 8 m depth. Mineralogy, petrography and X-RD analysis on opal and host rock have been done prevailing that the Banten opal is opal – CT associated with zeolite (clinoptilolite). The opal has shatter cracks and colloform structure with good quality of opal. Keyword : Banten opal, zeolite, opal-CT Field Wise Seminar, Geo UGM 2006