CHARACTERISTICS AND QUALITY ENHANCEMENT OF PRECIOUS OPAL FROM ETHIOPIA AND FIRE OPAL FROM MADAGASCAR

Abstract

Precious opal from Ethiopia and fire opal from Madagascar were collected and analyzed for properties and characteristics prior to experimental enhancement. The main aims of this study are to search for the proper method of opal enhancement and to recognize the specific characteristics yielding gemological feature. Raman spectrometer indicates that the Ethiopian precious opals are typical opal-CT whereas Malagasy fire opals is opal-C. Microstructures of Ethiopian precious opals reveal bigger hydrated silica sphere (about 50-200 nm in diameter) with imperfect stacking which may lead to its weak play of color phenomenon compared to those found in Australian precious opals. On the other hand, Malagasy fire opal presents tiny hydrated silica spheres (about 10-100 nm in diameter). After enhancements with various methods such as heating, water boiling and oil boiling at 100°C, all groups of opal appear to have been changed, differently. The Ethiopian precious opals may have more intense in play of color phenomena after heating and water boiling, properly. Malagasy fire opals appear to have no change after all enhancement techniques. The hydrated silica spheres of Ethiopian precious opals have turned to more perfect form. In conclusion, heating is quite effective enhancement for the Ethiopian precious opals due to property of hydrophane. Malagasy fire opal should have no potential for enhancement. The best enhancement of precious opal in this study is heating and boiling because it can improve play of color phenomena.