The Queen of Gems is the name often acquainted with opal. The stone is a silicon oxide and is closely related to Chalcedony which is one of the least expensive gem materials. Opal is softer then the quartz gems and it contains a variable amount of water in its composition. It is also much more fragile then the quartz gems. Opal jewelry is much desired because of the stones unique and distinctive play of color, called "fire". Its unique properties and delicate beauty have made the stone a treasured possession since ancient times. The majority of the stone is rather dull and lifeless and is referred to as "common opal". With color variations from gray to yellowish, the common variety has little or no gem value.

Gem opal is categorized into four types: White opal much resembles porcelain in appearance with its opaqueness and white color. Speckles and arrays of rainbow color appear in the stone and is the most common of the types to be used in opal jewelry. Black opal is very rare and very costly. This variety also contains fire but the coloration is dark gray or black which produces a stunning effect in the accentuation of the color play. Water opal is basically colorless and transparent in appearance but does exhibit an array of brilliant flashes of color within it. Fire opal has an orange or red body color and is also transparent or translucent in appearance. The presence of fire within the stone may or may not be displayed.. Many of these reddish and orange stones may not exhibit any fire at all. This type is also quite commonly used in the making of opal jewelry.

Without a doubt, the finest quality and most revered opals come from Australia. The Australian black variety can sell upwards of $1000 per carat as compared to a few dollars to a few hundred dollars a carat for the white variety. Other gem quality material comes from Honduras, Mexico, Brazil and the Virgin Valley in Nevada. When purchasing opal jewelry, keep in mind that the stone is rather soft and fragile and is far more suited for items such as brooches, pendants and earrings that generally take less stress during every day wear.