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Boulder Opal Facts, Information and Description Boulder Opal Facts and Information

Boulder Opal Facts and Information

Boulder Opal Facts, Information and Description

The gemstone Opal is the official October birthstone as adopted by the American National Association of Jewelers in 1912. It is also the birth stone for the Zodiac sign of Libra. See the birthstone tables for additional references to this stone. Boulder opal is found in Australia where precious opal forms in veins and patches within brown ironstone boulders. When the opal is mixed through the ironstone it is called matrix opal. Hardness ranges between 5.5 and 6 on the Mohs scale. Boulder opal is very durable due to the ironstone backing the opal forms on.   Because water content within the opal is very low it almost never cracks or crazes as it ages.

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.

Boulder opals are graded into specific groups (listed below) which have been defined by the Australian Gemological Association:

Boulder black opal
Boulder crystal opal
Boulder light opal
Boulder matrix opal
Yowah nuts

Boulder splits
Seam and vein opal
Sandstone opal
Pipe opal
Wood opal

Light opal is the most common type of opal found and refers to both the crystal type opal (translucent) and the milky opal (opaque). It is the most common variety of opal and is generally less expensive than gem quality light opal. Brilliantly colored light opals may be quite expensive with a value exceeding some Black and Boulder Opals.

Brilliance or luster is one of the primary factors that determine an opal's value. An opal with strong intensity and color play adds more value.

Rumor and Legend Surrounding Australian Opals:

A long standing rumor is that boulder opals are porous and will absorb moisture, such as perspiration but an Australian opal is not porous and will not absorb moisture. To change the water content locked in an opal's tiny voids it must be heated extreme temperatures. Opal's hardness on the Mohs scale is 6.5.

Opal takes its name from the Latin word Upala meaning precious stone. The Roman scholar Pliny described opal as having the fire of carbuncle (a deep red garnet) and the brilliance of amethyst with the green color of emerald. The Romans believed opal was the symbol of hope and purity. They called it cupid paederos (child as beautiful as love) and thought the wearer safe from disease.

The Arabs believed that opals fell from heaven in flashes of lightning. Ancient Greeks also believed the opal had the power of giving foresight and the light of prophecy to their owners. Cleopatra is said to have worn an opal to attract the attention of Mark Anthony.

Aborigines believe they have lived in Australia since the beginning of all creation. This culture has produced many myths and legends about opals over this span of time and the Aborigines believe the opal has a spiritual value. They believe the opal represents something an ancestor left behind as a sign of his or her presence. The Wangkumara people have a legend which tells how their people gained fire from opal stones, with the assistance of a Muda - a Creator who switches from human form to pelican.

This story is preserved in a book of Aboriginal legends, titled 'The Opal that Turned into Fire', compiled by Janet Mathews and published by Magabala Books. This legend recounts how the Wangkumara people decided to send a pelican (Muda) to explore the Northern Territory, so he could return and tell them what was there. The pelican set off with all the fish and water he would need for the journey stored in the pouch beneath his beak. After flying a while the pelican felt ill and landed on top of a hill that the Wangkumara later named Bildimini. While resting the pelican observed the ground beneath him and was amazed by its magnificent array of colors.

Although he did not know it, what he saw was opal. The pelican was so curious he began to peck at the colored stones with his beak. Suddenly, a spark flew out and lit the dry grass nearby. The flames rose and spread slowly across the plains approaching a group of Wangkumara who were camping near Cooper's Creek. The people were able to use the fire to cook their meat and fish for the first time, and were grateful for this new gift.

Another legend tells how an earlier Muda, also in pelican form, created Cooper's Creek for the Wangkumara and filled it with fish. Wounded by a spear, this Muda died on the hill that would be called Bildimini. His blood and the water in his pouch flowed down the hillside, soaking into the earth and hardening into opal and gold.

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