An early confession – my October birthstone is opal! And I LOVE opals. I don’t think there is any other stone that comes near an opal for beauty, vibrancy and range of color.
They are unique among gemstones due to their ability to display a vast array of colors within a single stone, a phenomenon known as “play-of-color.” This feature makes opals highly desirable and valuable in the world of gemstones.
An opal is a hydrated amorphous form of silica, which means it lacks a defined crystalline structure, such as hexagonal or orthorhombic. Its water content can range from 3% to 21% by weight, but is typically between 6% and 10%. The internal structure of a quality opal causes it to diffract light, resulting in the play-of-color. This can produce flashes of rainbow hues that shift and change as the stone is moved. Opals come in a variety of colors, including white, black, blue, green, and even red, each offering a unique visual appeal.
The name “opal” is derived from the Sanskrit word “upala,” meaning “precious stone.” This was later adapted into the Greek “opallios,” which translates to “to see a change of color.” This etymology reflects the gemstone’s defining characteristic: its captivating play-of-color.
Opal background color can be white, black, or clear. Crystal opals are defined by their clear background. An opal’s play-of-color can range from subtle glimmers to vivid bursts of neon hues. The quality of the play-of-color has the most influence on an opal’s value, however other factors are also considered:
- Color – The more vibrant and diverse the colors, the more valuable the opal.
- Pattern – The arrangement of colors in the opal can affect its value. Rare patterns such as “harlequin” (a checkerboard of colors) are highly prized.
- Clarity and Transparency – Opals can be opaque, translucent, or transparent. While some opal types are valued for their opacity, transparency can enhance the visibility of the play-of-color.
- Cut – The shape and surface quality of the opal affect its aesthetic appeal. Skilled cutting can maximize the play-of-color and overall appearance.
Opals are relatively soft gemstones, and their hardness varies depending on the type of opal. Here’s a breakdown of the hardness of different types of opals on the Mohs scale:
- White opals: 5.5-6.5 (medium to soft)
- Black opals: 5.5-6.5 (medium to soft)
- Fire opals: 6-6.5 (soft to medium)
- Boulder opals: 6-6.5 (soft to medium)
- Crystal opals: 6.5-7 (medium to hard)
Opals are generally considered to be relatively soft gemstones, which means they can be scratched or damaged easily. There are still suitable for jewelry, but do require some special care. Here are some tips to keep in mind:
- Avoid harsh chemicals: Opals can be damaged by exposure to harsh chemicals, such as bleach or ammonia. Avoid cleaning your opal jewelry with these chemicals, and instead use a mild soap and water solution.
- Avoid extreme temperatures: Opals can be damaged by extreme temperatures, such as those found in ovens or freezers. Avoid exposing your opal jewelry to these temperatures.
- Avoid scratching: Opals are relatively soft, so they can be scratched easily. Avoid wearing your opal jewelry in situations where it may be prone to scratching, such as when gardening or doing other activities that involve rough surfaces.
- Clean regularly: Opals should be cleaned regularly to remove dirt and oils that can accumulate on the surface. Use a soft cloth and a mild soap solution to clean your opal jewelry.
- Consider a protective coating: If you’re concerned about the durability of your opal jewelry, consider having a protective coating applied. This can help to protect the opal from scratches and damage.
Overall, opals can make beautiful and unique jewelry pieces, but they do require some special care to maintain their beauty and durability.
Black Opals
Among the various types of opals, black opals are the most prized and valuable.
Black opals are generally rarer than white opals because they require specific geological conditions to form. They are often found in areas where there has been significant tectonic activity, such as in the Lightning Ridge region of Australia. Black opals contain a higher amount of iron oxide (FeO) than white opals – white opals have a higher silica content (SiO2) than black opals. The iron oxide is responsible for the dark, iridescent colors and the characteristic “play-of-color” effect in black opals. This dark body tone makes the play-of-color stand out more vividly compared to lighter opals.
Black opals are not only valued for their beauty but also hold a special place in jewelry and gemstone collections around the world due to their rarity and unique visual appeal.
Unique Features of Black Opals:
- Intensity of Color – The dark body tone of black opals allows for a more dramatic play-of-color, often displaying intense blues, greens, and reds.
- Rarity – Black opals are much rarer than other types of opals, contributing to their higher market value.
- Patterns – Black opals often exhibit unique and intricate color patterns, such as pinfire, flash, and rolling flash patterns.
