The Opals

There are three main types of opals:

• Precious opals , which display multiple colors on the surface thanks to a phenomenon of light diffraction.
• Fire opals , transparent in yellow, orange or red color.
• Common opals , without play of light and which are colored in the mass.

In all cases, it is silica organized into microscopic beads. What differentiates them is the way in which these beads are arranged.

1 Precious Opals

Precious opals are among nature's most fascinating stones. This gemstone is distinguished by its ability to reflect an incredible palette of very vivid hues. All the colors of the rainbow can be found in them. This is normal because it involves the same phenomenon, namely light diffraction. The colorful phenomenon is due to the fact that the silica microbeads are locally the same size. Each color is defined by a bead diameter. Therefore, the different color schemes correspond to areas in the stone where the beads are the same size.

The color and opacity of the background also vary greatly. It can be transparent, translucent, or opaque. The transparency of an opal is determined by the purity of the silica and the size of the microscopic beads.

Its color ranges from colorless to milky white, sometimes with orange to brown hues. A pristine, opaque white is highly sought after. Finally, there is the black background, which particularly highlights the play of color. These are the most expensive and are mainly found in Australia, which is the most renowned country for opals. The other source of beautiful precious opals is Ethiopia.

In addition to Australia and Ethiopia, other countries known for opal production include Brazil and the United States. Nevada, in the United States, is known for its precious Virgin Valley opals, while Brazil produces high-quality fire opals and common opals.

Boulder Opals

Boulder opals are a special variety of precious opals. They feature remnants of the matrix where they grew. This creates opal veins that extend through the stone, which is usually brown to black. This results in a mix of vibrant colors and natural textures. These opals are primarily mined in Australia, particularly in the Queensland and New South Wales regions. Boulder opals gain their strength from their association with the parent rock. Each piece is unique, and they are highly prized by collectors and jewelry designers who seek distinctive and naturally beautiful pieces.

Hyalite Opal

Hyalite opal is distinguished from other opal varieties by its transparency and glassy appearance. Hyalite opal is transparent due to its relatively pure chemical composition and the absence or low presence of impurities that could obstruct light. The size of the silica microbeads is more disordered than in classic precious opals, which means they often do not offer a play of color.

Some Hyalite opals can still exhibit flashes of color in transmitted light (the stone is held up to a lamp), offering subtle and changing shades as the light passes through the stone. However, they show little or no play of color in reflected light, which distinguishes them from other types of precious opals. They are therefore rarely used in jewelry.

This opal can sometimes exhibit a fluorescent glow under ultraviolet light, adding to its unique appeal among gemstone collectors.

2 Fire Opals

Fire opals are quite impressive because of their vibrant color. They are generally quite transparent and range in color from pale yellow to red, with orange being the most common. The silica beads in fire opals are arranged in a more haphazard manner than in precious opals, which explains the lack of diffraction and therefore of play of color. Some may also exhibit flashes of color, but these are less visible than on a white or black background. They are mainly found in Mexico.

3 Common Opals

Common opals have an opaque and uniform color throughout their mass. Opals are found in blue, pink, and orange. These opals can still be attractive because they can have beautiful colors. The cause of the color is due to micro-impurities invisible to the naked eye. In common opals, the silica beads are all different sizes, which is why they do not exhibit a flash of color on their surface.

4 History of opal

Opals have been used in jewelry and ornaments since ancient times. The Romans already valued opals, considered them precious gemstones, and used them to create magnificent jewelry.

Opals were also highly prized in England, with Queen Victoria collecting them and giving them to her daughters for their weddings. However, in France, opals have long been associated with bad luck. This superstition dates back to Walter Scott's 1829 novel "Anne of Geierstein," in which a cursed opal causes the death of its wearer. This belief persisted until the early 20th century.

Today, opals are still highly prized for their unique beauty and are often used in rings, pendants, and earrings.

5 Processing, imitation and synthesis

Be careful, there are many treated stones or simply fakes on the market. Common treatments to improve the appearance of opals are fuming, impregnation, opal doublet, and opal triplet.

Smoking consists of exposing the opal to smoke which will color the background and accentuate the colors by contrast

Impregnation uses resins to strengthen the stone.

Opal doublets and triplets are assemblages of thin layers of opal with other materials to improve their durability and appearance.

There are some synthetic opals (identical in composition to natural opal but man-made), but they are not as common as sapphires and rubies.