Opal is a unique gemstone known for its delicate nature and varied color patterns that differ from stone to stone. Most opal jewelry comes from mines in Australia, where the first opal excavations began in the late 1800s. Opal forms as silicate spheres accumulate in sediment deposited in river beds, caves, and canals. These silicate spheres scatter light within the stone to create its colorful patterns. However, opal's high water content of 6-10% makes it very soft and fragile, ranking only a 6 on the Mohs hardness scale. Special care must be taken to prevent damage when wearing opal jewelry.