Gem quality opal is one of the most spectacular gemstones. The bright colors dancing around in this gem material can be quite captivating. Precious, Black, Fire, Boulder, Jelly, Crystal, White Opal are the basic types of opal. Australia has most of these verities and supplies most of the worlds opal supply. A jelly type of opal from Ethiopia is showing up a lot more these days. Opal has a hardness of about 5.5 to 6.0 on the Mohs hardness scale.