Opal is one of the most intriguing gemstones because of its many unique plays of color. Opal is a form of silica that contains 6-10% water. The "play of color" comes from light reflecting from the very tiny silica spheres. Although over 90% of opals come from Australia, some do come from Brazil and Mexico. Recently, opals have also been found in Africa. There are several types of opal including white opal, crystal opal, black and gray opal, boulder opal, jelly opal and fire opal.