Opal

Other Silicates & Gemstones

Opal is hydrated, noncrystalline silica and is therefore classed as a mineraloid rather than a crystalline mineral. Precious opal shows play-of-color when orderly arrays of microscopic silica spheres diffract light; common opal lacks this moving spectral display.

Identity

Material or variety: Opal
Scientific or material identity: Opal
Classification: Natural mineral or mineral variety
Composition or formula: SiO₂·nH₂O
Crystal system or structure: Non-crystalline (amorphous)
Geological or manufacturing origin: Can form in more than one geological environment, or combines several materials.
Mohs hardness: 5 to 6.5

Origins

Australia · Brazil · Canada · Ethiopia · Indonesia · Mexico · Peru · Tanzania · USA

Appearance & optical properties

milky white opal with small red, green and blue play-of-color.

History & discovery

The name reached English through Latin opalus and is often traced further to Sanskrit upala, meaning precious stone. Romans prized opal by the first century CE and admired its range of colors. After Australian deposits entered commercial production in the 1890s, Australia became its best-known source.

Uses & care

Common uses: Precious opal is cut for rings, pendants, earrings, and brooches. Common and lower-grade material is also carved or polished into beads and ornamental objects.
Handling and cleaning: Clean with warm soapy water. Avoid steam, ultrasonic cleaning, sudden temperature changes, prolonged heat, drying conditions, and hard knocks; opal contains water and can craze or fracture.

Jewellery

7 pieces of Opal jewellery. Learners earn each one in DigMyGem by learning words; until then it shows as a silhouette.

Andamooka Opal
Necklace
A 203-carat crystal opal mined at Andamooka in 1949 and cut by John Altmann. It was presented to Queen Elizabeth II during her 1954 visit to South Australia and set with diamonds into an 18-karat palladium necklet.
Flame Queen Opal
Jewel
A 263-carat red-on-black opal found at Lightning Ridge in 1915 and famous for its eye-of-opal fried-egg pattern. It was exhibited at the Geological Museum in London for the 1937 coronation of King George VI.
Olympic Australis
Jewel
The largest and most valuable gem opal ever found, a 17,000-carat stone unearthed at Coober Pedy in 1956 and named for that year's Melbourne Olympics. It remains uncut in the Altmann and Cherny showroom in Sydney.
Fire of Australia opal
Jewel
A 4,990-carat uncut opal from Coober Pedy, often described as the world's finest uncut opal. It was acquired by the South Australian Museum and displayed as a natural specimen.
Halley's Comet Opal
Jewel
The largest uncut black opal ever found, a 1,982-carat stone from the Lunatic Hill claim at Lightning Ridge, named after Halley's Comet. It remains a raw, unset collector's specimen.
Galaxy Opal
Jewel
The world's largest polished opal, certified by Guinness World Records in 1992; found at Brazil's Boi Morto Mine in 1976 and carved from a 5,205-carat rough stone into the shape of a child's head. The finished stone weighs about 3,749 carats and is held in a private collection.
Beverly the Bug
Jewel
The first known opal to contain an insect inclusion, an exoskeleton of a nymphal Hemipteran, found on Java in 2015 and authenticated by the Gemological Institute of America. It has been displayed at the Perot Museum in Dallas and the Alfie Norville Gem and Mineral Museum in Arizona.