Opals are one of the most unusual stones on earth. They are considered hydrated silicon dioxide, which means that their internal structure is a tight latticework of silica spheres with water molecules filling the spaces in between. This structure refracts light to create the beautiful gleaming colors that we associate with gem opals. The size of the spheres determines the colors that we see. Interestingly, gem opals can contain from 2 to 10 percent water, which can eventually lead some of them to crack if they dry out too much. For this reason, Heart of Stone Studio offers sturdier opals which have the gemmy portions safely fully or partially contained in matrix. We think that this protects the opal material better without sacrificing its color and overall beauty.