Opal, SiO2-nH20, is a gemstone that comes in many colors. The multi-colored flashes of light that opal emits give it a truly remarkable and valuable look. Care must be taken when wearing opal for jewelry as it is one of the softer gemstones, listed as 5 to 6 on the mohs scale of hardness. Opal is the birthstone for October. Under this heading, we will list only the white, black, blue and transparent opal types. Mexican fire opal is listed on a separate page. Finished opal jewelry can be viewed here. We have the following loose opal gemstones in stock: