Opal is a natural silica colloid containing 5-10% water. Unlike most gemstones, opals are amorphous. There are some unstable amorphous structures in opal, which will change color or even crack due to lack of moisture, but there are also opal with very stable structure, which will not change under normal environment. Opal is generally egg white, if mixed with other atoms, it can form various colors, such as opal containing iron, calcium, magnesium, copper, usually blue, green, yellow, red, etc. Among all kinds of gemstones, it is sought after by Westerners as one of the six gemstones because of its strong variegated effect. Opal usually has a glassy or waxy luster.
