Dropping a Knowledge Bomb

Here are some KB's about Pam101's Mom's birthstone...Opal's!

Opal is the modern October birthstone and the accepted gem for the 13th wedding anniversary.

Most opal is 50-65 million years old, dating back to the Cretaceous period when dinosaurs roamed the earth. Opal formed as silica from decomposing rocks mixed with ground water which formed a silica gel that collected and hardened in underground cavities and fissures. Opal's chemical formula is SiO2 .nH2O.

There are two distinct types of opal, common and precious. The way the silica particles form determines which type. In precious opal, silica particles are packed in regular rows and layers. Moving the stone causes light to diffract, or split, as it grazes the opal surface. This light diffusion shows iridescent flashes of green, blue, aqua and sometimes yellowish or red colors which are referred to as "fire".
Color and Varieties:

Black Opal comes from the Lightning Ridge region of Northern New South Wales. It is the most rare and valuable opal. Fine quality black opals often cost more per carat than diamonds. The term black opal is misleading because the opal is not actually black, but instead has a very dark base. This dark base enhances the brilliant colors known as "fire".

Boulder opal occurs in the boulder opal belt, an area between the New South Wales border and northwest Queensland. Boulder opal forms on a dark ironstone base (the host rock) and occurs as a thin uneven layer adhering to the ironstone. Because of the uneven layers, sometimes part of the ironstone is visible on the surface of the stone. Queensland Boulder Opal accounts for a small percent of the world market, and because of its brilliance and rarity can bring up to $1000 a carat.