Often referred to as the "Queen of Gems", Opal throughout history has been surrounded by mythological lure. From the Roman aristocrats to the Aztec rulers and eventually gracing the writings of Shakespeare, Opal has captivated a world of an audience.

So what is the nature of Opal?
Opal has a chemical composition of hydrated silicon dioxide(SiO2-nH20).Both the common and precious opal varieties are comprised of nanometer sized silica spheres and a water content ranging between 3- 10%, with some stones containing up to 20%. The Specific Gravity of Opal is 2.15 (+.08,-90),dependent on the density of mineral content. It has a Refractive Index 1.45 (+.020,-.080) and measures 5-6.5 on the Moh’s Scale of Hardness

What causes “Play of Color” in Opal?
The rare occurrence and phenomenal "Play of Color" observed in Precious Opal is derived through perhaps accidental perfection, the incidence of a three dimensional grid work of silica spheres. By viewing the gemstone at different angles,Precious opal can display a rainbow of colors through means of light diffraction, produced throughout and around the silica spheres. The size, stacking and concentration of the spheres will indicate the various colors and patterns observable in the gemstone.

Where does Opal come from?

Opal varieties carry distinctive characteristics from origin, location, and bodycolor. The two types of rock formations producing both common and precious varieties have been found through either sedimentary, or volcanic rock origins in different locations around the world.


Australia is the worlds major producer of Opal. The Great Artesian Basin spreading over the states of New South Wales, Queensland and South Australia, account for an estimated 90% of opal production.



Black Opal
Precious Black Opals reign among the opal varieties. The phenomenal beauty and play of color that radiates against a dark to black bodycolor, command the highest in value. Some of the most notable and phenomenal specimens of natural precious black opal have been mined in Lightning Ridge, Australia. The United States, in particular Virgin Valley, located in Northern Nevada has also produced stunning and brilliant specimens of black opal.


Boulder Opal & Yowah Nuts
The state of Queensland, Australia is home to Boulder and Yowah Opal, often referred to as “Yowah Nuts”. Yowah nuts are a form of Opal in Matrix, while Boulder Opal can be found both in Matrix or as seam opal, a thin layer of opal attached on ironstone.

The natural formation of thin veins and seams within the host rock, composed mainly of ironstone, give this opal it’s distinct brown bodycolor. Due to the brittleness of the seams and thin veins, the opal cannot be extracted, and in turn gives these opals those embedded, opal in matrix characteristics.

White Opal
Perhaps the most popular and commonly used in jewelry is White Opal. Coober Pedy, amongst other surrounding areas in Southern Australia, are the worlds major producers of natural white opal.

Crystal Opal
Crystal opal can be identified by its transparency. This seemingly pastel brushed crystal opal to the right is from the Mintabie mines of Southern Australia.The uniqueness of Opal rough from this area can be indentified by a sandy layer over the body, a little different to the touch from the potch (host rock) that covers opals from other areas of Australia.

Fire Opal

Fire opals are distinct by their transparency of rich, fiery, bodycolors of red and orange, with some lighter stones exhibiting a warm yellow glow. Some fire Opals can exhibit play of color throughout the body, such as this opal to the right, which shows specks of fire floating within the stone. They can be faceted or cut into cabs, such as the fire opal in rhyolite matrix to the left, also referred to as "Cantera Opal". Being the national gemstone of Mexico, once referred to as "quetza-litzle-pyo-llitli" by the Aztec gods , it is found in varoius locations throughout the country, with some of the most prominent mines located in the states of Jalisco and Queretaro.


Black Matrix Opal
Another beautiful and unique variety of Opal known as "Black Matrix Opal" is mined in Honduras. These beautifully speckled, galactic appearing Opals are of volcanic origin, forming in basalt belts, which gives them their natural black bodycolor.

Ethiopian Opal

Ethiopian Opal has a beauty all in it is own class, with a variety of striking play of color. Often seen are natural leopard like prints (a comlumnar structure), a unique attribute in Ethiopian Opal. A newer source of Ethiopia Opal has been discovered in the Wollo region, known as Ethiopian Welo Opal or Wollo Opal. Unlike the rich ,brown bodycolor often seen in Ethiopian Opals from other regions, Welo Opal comes in a variety of bodycolors from blue, white, crystal, light brown and black.


Common Opal

Common Opals come in a variety of bodycolors to choose from. They are very popular and more affordable compared to the precious varieties and often seen as beads and larger cabs. What sets them apart from the precious varieties is their absence of fire. The Pink Opals on the right have a delicate, pretty and soft glow to them. The color personally reminds me of a light strawberry milkshake!


From rough to Gem
An Opal in the rough is a rare beauty waiting to be revealed. The art of uncovering the layers of vibrant colors is a reward in itself. After the cutting and polishing process, we feel each opal emerges with its own unique “personality” as we like to refer to it, and truly, no Precious Opal is exactly the same in appearance as another.
The following information is a grading reference for Black, Dark and White Opals:
Bodytone
The color of the natural backing is what gives Opal their bodytone. The following chart gives a description to the grading of bodytone.



Play of Color
The largest amount of color observable on the Opal face up is what determines the dominant hue of the stone, followed by the other underlying hues as you turn the stone at different angles. The most valuable and rare is "Red fire", followed by violet, orange, yellow, green and blue. Opals displaying multi colors are generally more valuable then single color stones taking into consideration the brillliance of the stone and the hue, tone and saturation of the colors.

Transparency
Transparency refers to the transmission of light through the stone. You can see in the crystal opal to the left the light coming in through the back of the stone. In contrast, opaque stones, have no light transmission.

Pattern

Cut

Opal Treatments
In the gem trade, it is mandatory to disclose treatments of gemstones. Opal, like many other gemstones can undergo treatment to enhance its potential beauty.Treatments such as a mixture of sugar and sulfuric acid, smoke treatments, waxes and resins can be applied to a not so favorable specimen in order to enhance beauty and value. As lapidarists, we at Pearla del Mar do not look so well on these procedures, and we feel natural opals should remain in their natural color, before and after the cutting and polishing process. On the majority of our Opals, we use Cerium Oxide to polish, with the exception of Honduran Black matrix, we use Tin Oxide for polishing.