This item is an intarsia doublet of black onyx and blue-green Opal .
This gemstone measures 17mm x 12mm and is 5mm thick and weighs 12.5 carat.
The opal used in this intarsia is Australian and is a nice bright blue green with some flashes of red. This is a very unique gem and clearly it would work up into a beautiful ring set in sterling or karat gold.
Intarsia is the name for an inlay of gem materials of different sizes and shapes that are fitted together with precisely cut edges, so that there are no gaps between the stones. These pieces are usually assembled on a flat, thin surface of onyx or jade as a base. They are then glued onto this surface and the top of the assembled piece is ground flat and polished. The result can be a striking pattern of color, depending on the gem material used. The overall shape can then be determined with further lapidary work. This is a great way for a cutter to utilize smaller pieces of stone left over from previous projects that are too small to fashion into a cabochon. For the jeweler, it is an opportunity to utilize these Intarsia cabochons to create striking and unique designer jewels.