Prelimanary Study Of Opal Genesis At Lebak Regency, Banten

Precious opal is a famous gemstone because of it’s internal display of colour, rare and expensive. Lebak Regency famed for gemstone colectors. Among all kinds of gemstones, black opal is the most precious one. It has very good internal display of red, pink, blue, green and purple colour. However the occurrence and genesis of this opal is still unknown. Prelimanary study has been done in this area. Based on petrology and stratigraphy data, the host rock of opal is black gray claystone, soft and fracture under conglomeratic and pebbly sandstone with cross bedding and channelling structure. From petrographic analysis, the host rock is tuffaceous claystone with rich of altered and devitrified glass. The opal shows perlitic, shatter cracks, bedded and colloform sructures that indicate distinctive feature of silicate colloidal origin. ICMERS Proceeding, UPN 2004