Opal is the birthstone of October. A gemstone comprised of silica and water, it gets its famous iridescence from the infinitesimal silica spheres inside of its structure. These spheres are the same size and closely packed together, but the arrangement is not crystalline. Opal is one of the few gemstones whose structure is amorphous, or non-crystalline. The main color of an opal can be white, black, gray, yellow or orange, blue pink, green or brown.
Types of Opal
The several types of opal. They include:
• Precious opal, which contains areas of iridescence on a body that can be transparent to dark.
• Common opal, which lacks this iridescent but can come in a range of colors, including pink and blue.
• Fire opal, which is orange or yellow, and may or may not have patches of iridescence.
• Water opal, which is clear and nearly colorless, but has an internal iridescence.
• Dendritic opal, which has inclusions that resemble trees.
A cat's eye effect can also be seen in an opal, but this is rare. A cat's eye is a streak of light that's caused by the way light behaves on tiny needles in the gemstone.
Boulder and matrix opals are opals found inside the host rock. In boulder opal, the opal is found in a flat area on top of the rock. In matrix opal, the gemstone is found in fissures in the rock.
How They're Cut
Most opals are cut as cabochons or carvings, though transparent fire opals are sometimes faceted. The most expensive type of opal is a high quality black opal, which is actually a very dark blue. Fire opals are the second most expensive type and white opals are the third most expensive. The most sought after opals have a strong play of light over the entire stone and contain all the colors of the rainbow. Violet is the most common iridescent color, while red is the least common. Even though dendritic opals have some value, the ideal opal is free of inclusions.
The Qualities of Opals
Opals are rated a 6 on the Mohs hardness scale, with diamond, the hardest material, being a 10. The gemstone’s worth is determined by its size, body color, iridescence and transparency. Because opals contain water, they might crack if they're allowed to dry out.
Opals have been valued as gemstones since the time of ancient Rome. They are set in rings, necklaces, earrings and brooches. However, opals need to be protected when they're not worn. Place them in their own felt bag or a separate, felt-lined till in the jewelry box. They should be cleaned with a damp cloth or rinsed with warm water and mild soap, but never allowed to soak. They shouldn't be cleaned with ultrasound equipment, as this may ruin their iridescence.
Opals should never be worn when cooking, cleaning, swimming or doing anything that would expose them to harsh chemicals or great changes in heat or humidity.
The name opal probably comes from the Sanskrit "upala" which means “precious stone.” Good quality opals are found in Australia, the Czech Republic, Mexico, Peru, Ethiopia, Brazil, Honduras and the United States. Australia is known for the quality of its black and white opals, while Mexico is known for its fire and water opals.
Some people believe that opals are bad luck, and Alexandra, Queen of England, famously replaced the opals in her tiara after the death of her mother-in-law Queen Victoria. But of course, opals are not bad luck!
Our professionals at John S. Cryan jewelers are pleased to offer quality opals to our customers. Visit our store at 673 2nd Street Pike, Southampton, Pennsylvania, or give us a call at (215) 357-8850.