Opal's make up is silica spheres and water, packed in layers. (Approximately 10% of an opal is water.) Light breaks into a spectral of colors from the light refracting between the layers. The silica sphere's size, determines the colors. Large spheres display all the colors; smaller spheres display the blue-violet range.
Opals are not a good choice for rings because they are very fragile. A quick change in temperature, or a slight blow may break the stone. Because this gem contains water, the water may evaporate there by shrinking the opal slightly, causing stress to the stone that is relieved by cracking. This is known as crazing.
Opals do well in pendants. Wearing them close to the body protects them, they are safe from scratching, and the temperature is even. They also absorb some moisture from the body so they don't lose water. Opal will retain its beauty if it is worn often. Opal is the birthstone for October, and the 14th and 18th anniversary.
