Opal Stones and Gems: Value, Price, and Jewelry Information

view gemstone encyclopedia

Opal, 3.51 cts, 1.3 x 1.2 x 0.5 cm, cut by Spectrum Award-winning faceter Mark Kaufman. Tsehay Mewcha, Wegeltena, Delanta Woreda, South Welo, Amhara Region, Ethiopia. © Rob Lavinsky, www.iRocks.com. Used with permission.

Opals are in a class by themselves. As a species, opal is so unique it has its own descriptive vocabulary. More than any other gem, each opal is distinctly individual. Opals are also the most delicate gemstones commonly worn and require special care.

Opal Stone Value

Start an IGS Membership today for full access to our price guide (updated monthly).

Black Opal - Tone N1 to N4

1 to 5 carats
Below Commercial
- /ct
Commercial
- /ct
Good
- /ct
Fine
- /ct
Extra Fine
- /ct
5 to 10 carats
Below Commercial
- /ct
Commercial
- /ct
Good
- /ct
Fine
- /ct
Extra Fine
- /ct
10+ carats
Below Commercial
- /ct
Commercial
- /ct
Good
- /ct
Fine
- /ct
Extra Fine
- /ct

Dark Opal - Tone N5 to N6

1 to 5 carats
Below Commercial
- /ct
Commercial
- /ct
Good
- /ct
Fine
- /ct
Extra Fine
- /ct
5 to 10 carats
Below Commercial
- /ct
Commercial
- /ct
Good
- /ct
Fine
- /ct
Extra Fine
- /ct
10+ carats
Below Commercial
- /ct
Commercial
- /ct
Good
- /ct
Fine
- /ct
Extra Fine
- /ct

Light Opal - Tone N7 to N9

Body Tone
N7
Below Commercial
- /ct
Commercial
- /ct
Good
- /ct
Fine
- /ct
Extra Fine
- /ct
Body Tone
N8
Below Commercial
- /ct
Commercial
- /ct
Good
- /ct
Fine
- /ct
Extra Fine
- /ct
Body Tone
N9
Below Commercial
- /ct
Commercial
-
Good
- /ct
Fine
- /ct
Extra Fine
- /ct

Crystal Opal

1 to 5 carats
Below Commercial
- /ct
Commercial
- /ct
Good
- /ct
Fine
- /ct
Extra Fine
- /ct
5 to 10 carats
Below Commercial
- /ct
Commercial
- /ct
Good
- /ct
Fine
- /ct
Extra Fine
- /ct
10+ carats
Below Commercial
- /ct
Commercial
- /ct
Good
- /ct
Fine
- /ct
Extra Fine
- /ct

Boulder and Matrix Opal

1 to 5 carats
Below Commercial
- /ct
Commercial
- /ct
Good
- /ct
Fine
- /ct
Extra Fine
- /ct
5 to 10 carats
Below Commercial
- /ct
Commercial
- /ct
Good
- /ct
Fine
- /ct
Extra Fine
- /ct
10 to 15 carats
Below Commercial
- /ct
Commercial
- /ct
Good
- /ct
Fine
- /ct
Extra Fine
- /ct
15+ carats
Below Commercial
- /ct
Commercial
- /ct
Good
- /ct
Fine
- /ct
Extra Fine
- /ct
Composite Opals

 

Doublets prices are usually 15% to 35% of the value of similar looking natural, (solid,) gem. However, they occasionally run as high as 50% of a natural opal if they are of exceptional quality. Triplets are only about 1% of the value of an equivalent natural and peak at $500.

Other Opal Types

Contra Luz

All Sizes
Contra Luz
to /ct

Fire Opals - Faceted

.4 to 1 carat
Faceted
to /ct
1 to 5 carats
Faceted
to /ct
5 carats plus
Faceted
to /ct

Fire Opals - Cabochons

.4 to 2 carats
Solid
to /ct
In Matrix
2 to 10 carats
Solid
to /ct
In Matrix
to /ct

Pink Opal

All Sizes
Pink Opal
/ct
View Opal Stone Profile

The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.

Evaluating precious opal is a highly refined art. For details, see our articles on Appraising Opals and our Opal Buying Guide.

opal bracelet, Ethiopia - opal gems

78 opal cabochons from Welo, Ethiopia (52 ctw) in 18k gold bracelet. © Rob Lavinsky, www.iRocks.com. Used with permission.

Opal Stone Information

Data Value
Name Opal Stone
Varieties Common Opal, Agate Opal, Andean Opal, Cacholong Opal, Girasol, Honey Opal, Hyalite, Hydrophane, Jasper Opal, Milk Opal, Moss Opal, Pink Opal, Prase Opal, Semiopal, Wax Opal, Wood Opal, Fire Opal, Precious Opal, Black Opal, Boulder Opal, Crystal Opal, Harlequin Opal, Matrix Opal, Water Opal, White Opal
Crystallography Amorphous. Recent work shows that opal is composed of an aggregate of tiny spherical particles, that is, a solidified gel; often forms concretions; botryoidal; reniform; stalactitic.
Refractive Index 1.37-1.47
Colors Colorless, white, yellow, orange, and red (various shades), yellowish brown, greenish, blue, gray, black, violet.
Luster Vitreous, waxy, pearly.
Polish Luster Vitreous to resinous
Fracture Luster Waxy, subvitreous
Hardness 5.5-6.5
Wearability Poor
Fracture Conchoidal to uneven
Specific Gravity 1.99-2.25. (Orange-red variety, ~2.00; black and white opal, 2.10; green opal, 2.12).
Birefringence None
Cleavage None
Dispersion Very low
Heat Sensitivity Very
Luminescence Green fluorescence in opal often due to included U minerals. Much opal fluoresces strong white in SW, LW, sometimes with persistent phosphorescence. (See table below.)
Luminescence Present Yes
Luminescence Type Fluorescent, Phosphorescent, UV-Long, UV-Short
Enhancements Impregnation, dyeing, surface coating.
Typical Treatments Dyeing, Infusion/Impregnation, Surface Coating
Special Care Instructions Very heat senstive, clean with warm or room temperature soap and water. Avoid wearing gem where it will get rough treatment.
Transparency Transparent to opaque
Absorption Spectrum Most none. Green line at 660 nm, cutoff at 470 nm.
Phenomena Play of color. In rare cases, can display chatoyancy or asterism.
Birthstone October
Formula SiO2 · nH2O. Water= 1-21% in opal, usually 6-10% in precious opal.
Pleochroism None
Optics Isotropic; N: 1.44-1.47. Mexican opal as low as 1.37, usually 1.42-1.43.
Etymology From the Latin name, opalus, for this stone, possibly derived from the Ancient Greek opallios for "color changing."
Occurrence In sedimentary rocks or where low temperature solutions bearing silica can percolate through rocks.
Art Nouveau pendant

Nature scenes and animals were popular motifs in Art Nouveau jewelry, and opal gems were popular jewelry stones during this period. In this pendant by René-Jules Lalique, two enamel peacocks stand on a triangular opal cabochon. Gold, enamel, opal, pearl, and diamonds, 7.6 x 6 cm. France, circa 1901. Gift of Clare Le Corbeiller, 1991. Metropolitan Museum of Art, New York. Public Domain. (Cropped to show detail).

Opal Stone Facts and Information

For thousands of years, people have mined and treasured opals. These striking gems have inspired a rich body of folklore. (So rich, in fact, opal gems have been considered both the luckiest and unluckiest stones you can wear). Nevertheless, some scholars believe many ancient references to opal may actually have been to other gems, such as the iridescent iris agate.

Black Opal, Australia (Stone in Bracelet ~ 20 carats) - opal gems

Black opal, Australia (stone in bracelet ~ 20 carats). Photo © Joel E. Arem, PhD, FGA. Used with permission.

What’s the Difference Between “Common Opals” and “Precious Opals”?

Opal is an amorphous form of silica, chemically similar to quartz, but containing 3% to 21% water within its mineral structure. Gem grade opals usually have 6% to 10% water content.

common and precious opalsOpal is a sedimentary stone. Under the proper conditions, water percolates through the earth, becoming rich in dissolved silicates. When water enters a cavity, it deposits the silicates as microscopic spheres, forming opals.

If the spheres are uniform in size and shape and neatly stacked, they will diffract light. These stones are called precious opals. If the spheres are random in size, shape, and arrangement, the results are common opals.

Common opals can have an opaque or glassy appearance with a waxy luster. Seldom cut, these stones come in a wide range of colors. Common opals are often fluorescent.

Precious opals, also known as “noble opals,” display fire or play of colors.

What Does “Play of Colors” Mean?

Opal’s characteristic fire, or play of colors, was long thought to be the result of iridescence. However, with the advent of scanning electron microscopes, we now know it’s a result of diffraction.  This phenomenon of flashing or moving colors due to diffraction isn’t related to the body color of the opal.

The particular colors seen in an opal’s fire depend on the size of the spheres and the angle of viewing. For example, black opal gets its color from volcanic ash, but inclusions have nothing to do with the play of color. That is due entirely to the tiny silicate spheres. They must be smaller than 1,500 angstroms (Å) for blue and violet colors, but no larger than 3,500 Å to produce oranges and reds. To put that in perspective, 20,000 spheres are about the size of the period at the end of this sentence. (An angstrom is one ten-billionth of a meter).

Please note that the term “fire” typically refers to a gemstone’s dispersion. While it’s acceptable to refer to an opal’s play of color as fire, it’s not acceptable to refer to gemstone dispersion as “play of fire.” Only opals show play of color.

opal ring with play of colors

Opal ring. Photo by Gyulfox. Public Domain.

What are Opalized Fossils?

Since opals grow by filling in cavities in the earth, sometimes they take the shapes of pieces of wood, bone, and seashells buried in the ground. In effect, opal replaces these organic materials. These opals are called pseudomorphs, materials with shapes unrelated to their chemical content.

Opalized wood is also called xylopal or zeasite.

opalized fossil

Rear view of the opalized Addyman fossilized plesiosaur at the South Australian Museum. Photo by Bahudhara. Licensed under CC By-SA 3.0.

Assembled Opal Gems

assembled opals - doublets and tripletsGem cutters can take opal pieces too thin to use as a solid gemstones and assemble them into doublets and triplets.

A doublet consists of a thin layer of precious opal glued to a black base. A triplet adds a transparent quartz cap and makes a good ring stone, because the hard quartz keeps the softer opal from scratching.

While purists prefer common opal for the base material, jewelers use many black materials, including old phonograph records.

Opal Triplet

Opal triplet: Australian rough, ceramic base, and quartz top (30 x 23 mm). Photo © Joel E. Arem, PhD, FGA. Used with permission.

Opal Varieties

Black Opals

Black opals have a black body color with fire, which is often spectacular against a dark background. Body colors can also be very dark bluish, greenish, or brownish. Please note that the term “black opal” may also refer to black potch (inferior opal material) covered with a thin layer of crystal opal, which lets the black show through later.

A black opal from Australia, illuminated from two positions. (Stone in ring approximately 10 cts). Photo © Joel E. Arem, PhD, FGA. Used with permission.

Gray or semi-black opal has light to dark body color with fire.

Semi-black opal

Semi-black opal: Australia (approximately 10 cts). Photo © Joel E. Arem, PhD, FGA. Used with permission.

White Opals

White body color with fire.

Water Opals

A transparent or colorless body that may have fire in it.

Crystal Opals

Colorless and transparent to semi-transparent in transmitted light, crystal opals have a rich play of colors in reflected light. Black crystal opals are transparent to semi-transparent with dark body color and play of color.

crystal opal pendant

14k gold pendant with 31-ct crystal opal. Photo by Dan Mekis, Red Carpet Opals. Licensed under CC By-SA 3.0.

Milk Opals

These translucent, milk white stones may also have yellowish or greenish color.

Fire Opals

Translucent to transparent with a yellow, orange, or red body color, these stones may or may not display a play of colors. The “fire” in their name refers to their body color, not to play of color. These stones are also called Mexican or sun opals.

fire opal gems

Fire opal, Idaho (11.74), Mexico (5.15, hyalite)// Mexico (0.76, 8.04). Photo © Joel E. Arem, PhD, FGA. Used with permission.

Boulder Opals

Thin seams of opal that form in ironstone, these gems come in many colors and show dazzling fire, backed by their brown ironstone matrix.

layered boulder opal

Layered boulder opal, about 3 cm in width. Photo by Dietmar Down Under. Licensed under CC By 2.0.

Contraluz Opals

Very rare, contraluz opals are usually found in Mexico but have also been found in Australia. These transparent opals show a play of color in both transmitted and reflected light.

A contraluz opal from Mexico, illuminated from front and back (approximately 4 cts). Photo © Joel E. Arem, PhD, FGA. Used with permission.

Hyalites

Hyalites or jelly opals are transparent to translucent, colorless or white, with a glassy luster and little to no play of color.

This brilliant cushion-cut, colorless hyalite lacks any play of color. However, it does have an interesting feature. It has a very strong green reaction to SW UV and even shows a slight yellow-green reaction in daylight. 7.08 cts, 16.9 x 10.9 mm, Brazil. © The Gem Trader. Used with permission.

Moss Opals

White to brownish and opaque, moss opals contain dendritic inclusions that resemble moss.

moss opal - Idaho

Moss opal, Idaho (5.70). Photo © Joel E. Arem, PhD, FGA. Used with permission.

Hydrophane Opals

Light-colored and opaque, hydrophane opals become transparent and show a play of color when soaked in water or oil. Sometimes they’re called “magic stones.”

Geyserite

Siliceous sinter or geyserite is glassy opal that forms around hot springs and geysers. These massive formations aren’t faceted for jewelry.

geyserite

Geyserite, Iceland (9 x 5.5cm). Photo by Didier Descouens. Licensed under CC By-SA 4.0.

Diatomaceous Earth

Tripoli or diatomaceous earth consists of fine-grained, powdery masses of opal or the siliceous remains of microscopic marine animals called diatoms. This material is often used in polishing agents and fillers.

Cacholong Opals

Often bluish white, translucent to opaque, and very porous, cacholong opals resemble porcelain. This stone, also called kalmuck agate opal, will actually stick to your tongue.

Jasper Opals

These reddish brown and opaque opals resemble jaspers.

Prase Opals

These green to yellowish green, translucent to opaque, common opals resemble chrysoprase. Chrysopal refers to a golden green variety.

praise opals

Prase opals. Photo by Aisha Brown. Licensed under CC By-SA 2.0.

Menilite

An opaque gray to brown opal with a concretionary structure.

menilite

Menilite, 9 x 6.8 x 4 mm, Plateau de Merdogne, Puy-de-Dôme, Auvergne France. Photo by Didier Descouens. Licensed under CC By-SA 4.0.

Tabasheer

An opaline (opal-like) silica found in the joints of some bamboo.

Girasol Opals

Semi-transparent to translucent with a moving, billowy light effect, girasol opals resemble moonstones.

Chrysocolla Opals

These opals get their blue color from finely disseminated inclusions of chrysocolla, a copper phyllosilicate mineral.

Liver Opals

Sometimes refers to brown, common opals.

Resin Opals

Yellowish brown common opals with a waxy to resinous luster.

resin opal

Resin opal. Photo by Aisha Brown. Licensed under CC By-SA 2.0.

Iron Opals

Red to yellow common opals.

Louisiana Opals

Composed of quartz, opal, and pyrite, these gems occur in the state of Louisiana.

Oolitic Opals

These opals have small black or brown spherical inclusions resembling fish roe and an over play of color.

Wax Opals

Yellowish opals with a waxy luster.

Star Opals

Extremely rare, the asterism or star effect these opals display is caused by imperfections in the arrangement of their silicate spheres. Thus, their star effect differs from that of other gems such as sapphires, caused by inclusions.

Natural Opalite

The term “opalite” usually refers to a plastic or glass opal simulant. However, there is a variety of natural opal sometimes called opalite. This common variety of opal comes in green, lavender, or purple colors and can also show a cat’s eye. To avoid confusion, don’t refer to this opal variety as “opalite,” due to the name’s strong association with simulants.

Fluorescence in Opals

  • White Cliffs, Australia: medium blue (LW); may phosphoresce in LW.
  • Park, Wyoming: dull white (SW), strong white (LW); may phosphoresce in both SW and LW.
  • Queretaro, Mexico: dull white (SW), bright blue (LW); may phosphoresce in both SW and LW.
  • Virgin Valley, Nevada: bright green (SW), medium green, blue-white (LW); may phosphoresce in LW.
  • Quartzite, Arizona: pale yellow (SW), bright pale yellow (LW); no phosphorescence.

Opal may also fluoresce brownish. Black opal is generally inert. Fire opal luminesces greenish brown. Common opal often fluoresces green.  Natural opals may also have phosphorescence.

Opal Stone Vocabulary 101

Patterns

Descriptions of opal are as broad as the human imagination. The patterns seen in opals may resemble stained glass windows, butterflies, birds, and other natural and human-made forms. The most commonly used terms include the following:

Chinese Writing Chinese writing resembles Asian script. Usually in gold and green, somewhat rare.
Fern Leaf Fern leaf lacy patterns resemble a fern leaf. Mostly in larger green gems, rarely red.
Flagstone Flagstone features large, broad patches of color, set close together. Much like harlequin, only with larger patterns. Rare and highly valued.
Flame Opal Flame opal, bands or streaks of red fire that move across the surface.
Floral Floral, a variety of repeated designs and colors, reminiscent of floral dress material.
Harlequin Harlequin or mosaic, close-set broad patches  with angular play of color. Highly desirable, adds considerable value.
Palet Palette has a variety of colors, resembling an artist’s paint palette.
Peacock Opal Peacock opal, predominantly green and blue play of color, with some resemblance to a peacock tail.
Pinfire Pinfire or pinpoint, very small areas of fire set close together. Common and one of the less valuable patterns.
Rolling Fire Rolling fire, a rare phenomenon where the fire moves across the surface rather than flashing on and off.
Ribbon Fire Ribbon, slightly curved, parallel bands of color. Usually parallel and on black or dark base. Rare.
Straw Straw resembles flattened straws, crisscrossing each other. Rare.
Windmill Windmill, a pattern of fire that radiates around a central point. Very rare.
  • Chaff, thin, linear bands of color.
  • Flash opal, a play of color that quickly flashes off and on as the stone is moved.

Terms for Color and Color Distribution in Opal Gems

Onyx Opal and Agate Opal

These stones have alternating layers of precious and common opal. In chatoyant or cat’s eye opal, the color play is concentrated in the form of an eye or band.

Matrix Opal

Matrix opal consists of specks of precious opal in a rock matrix, usually sandstone. This type of opal is often dyed black to enhance the color play. Ironstone opal forms in a hard, brown, compact type of sandstone.

Matrix opal may also consist of layers or stringers of opal in a rock matrix. Also called mass opal.

Other Terms

Also gold opal (gold fire), blue opal (bluish fire), lechosos opal (green colors).

gold opal

Gold opal. Photo by Aisha Brown. Licensed under CC By-SA 2.0.

How Can You Identify Synthetic Opals?

Synthetic or lab-created opals are real opals, but they’re grown in laboratories instead of underground. They undergo the same formation processes, only at an accelerated rate in controlled settings.

Synthetic opals may show a strong display of color, usually in a mosaic pattern. With high magnification and top or backlighting, you can find a cellular, scale-like, snake skin, or chicken wire structure in the pattern. Under high magnification with transmitted light, synthetics may show a dendritic structure.

Gilson opals - synthetic opal gems

Opal gems synthesized through a process created by Pierre Gilson appear very natural. Gilson opals: cabochons from 3 to 6 cts. Photo © Joel E. Arem, PhD, FGA. Used with permission.

Synthetic opals don’t phosphoresce. They may also stick to the tongue. Synthetic white opal can show columnar structures from the side.

synthetic opal

Synthetic opal. Photo by Christian Schröder. Licensed under CC By-SA 3.0.

For more information on different varieties of synthetics, read our guide to synthetic opals.

How Can You Detect Faux or Imitation Opal Gems?

Unlike lab-created opals, imitations only simulate the appearance of opals. These imitations are typically made from plastic or glass.

Plastic imitations or simulants are soft and can be probed with a sharp needle. They don’t phosphoresce.

Glass simulants typically contain glass bubbles and swirl marks. They also don’t phosphoresce. Their specific gravity (SG) and refractive index (RI) are usually higher than natural opal.

Common Opal Enhancements

Vendors may treat low-quality opals to improve their appearance (and increase their prices). Although these processes may create beautiful gems, some of these enhancements may not last long. All of these enhancements should be disclosed before any sale. For more information, consult our guide to detecting opal treatments.

Oil, Wax, or Plastic Impregnation

Improves play of color, disguises crazing. Common, but stability poor for oil and wax. Detectable with a hot point test. Plastic usually requires major lab equipment.

Black Plastic Impregnation

Gives appearance of black opal, disguises crazing. Somewhat common with excellent stability. Detectable because the treated pieces have too low SG values and the concentration of color in cracks. May require major lab equipment.

Smoke Impregnation

Darkens body color. Common, but only poor to fair stability. Detectable through magnification and low SG (may float in water until it absorbs enough to sink). Loses play of color when wet but returns when dry. Unusually low RI, 1.38 to 1.39.

Aniline Dye, Silver Nitrate, or Sugar Treatments

Darkens body color. Common with good stability. Magnification shows black concentrations.

Advice on Hydrophanes

Hydrophane opals will absorb water and chemicals, which can have a negative effect on their appearance. Keep them dry and away from all sources of contamination.

Notable Sources for Opal Gems

Australia

Australia is the best known opal-producing area in the world. However, the deposits have been worked so intensely that they’re becoming depleted. Fewer miners are now working the opal fields compared to 10 years ago, and new discoveries are rare. These factors, plus worldwide demand, place tremendous pressure on opal prices.

The first discoveries of the modern Australian opal trade probably occurred around 1850, but Queensland yielded major finds around 1872.

Barion emerald-cut opal - Lambina Mines, Australia

1.47-ct Barion emerald-cut opal, Lambina Mines, Australia. © Dan Stair Custom Gemstones. Used with permission.

Types of Australian Opal

Australia produces various types of opals:

  • Boulder opal: shells of coarse, hardened, sandy clay with layers of opal in between.
  • Yowah nuts: walnut-sized concretions, in a regular layer, like a conglomerate. The opal is the central kernel and never reaches the outer edge.
  • Seam opal: thin to thick seams of white or black opal in sandstone matrix. Also known as sandstone opal. Large stones are very rare in this material.

Notable Australian Sources

Major finds of Australian opal are best known from specific localities, including the following:

  • Lightning Ridge: black opal in nodules, world’s finest of this material; first mined commercially about 1905.
  • Grawin Opal Field, about 25 miles SW of Lightning Ridge, produces light-colored seam opals.
  • Coober Pedy, South Australia: modern mining began here about 1915; only white opals found here, in sandstone and claystone matrix, but some very fine.
  • Andamooka, South Australia: opals found here about 1930; very distinctive opal, white and also brownish in color; may be artificially blackened to enhance the appearance of the fire in the matrix.
  • White Cliffs area: started about 1889, but the opal is usually small, with veinlets of precious opal within common opal.
  • Gabanintha (Murchison Goldfield): bright green opal, colored by copper, found in quartz.
  • Mintabie: mined since 1931, about 350 km northwest of Coober Pedy. This area has now been extensively prospected.
Freeform black opal gems

Black opal: Australia (freeform cabochons approximately 30 cts each). Photo © Joel E. Arem, PhD, FGA. Used with permission.

Brazil

Opal occurs in sandstone in Piaui Slate, northern Brazil, and also near Manaus, northern Brazil. The material is white and fiery and sometimes resembles good-quality Australian white opal. It ranks perhaps as the most durable opal, low in water and not heat sensitive. (Dr. Joel Arem reports seeing a cut gem held for 30 seconds over a candle flame with no adverse effects). The material seems to be abundant, and much of it is shipped to Hong Kong where it’s cut and sold, often as Australian opal.

yellow opal - Brazil

8.62-ct Brazilian yellow opal, 18 x 12.5 mm, oval buff top cut. © The Gem Trader. Used with permission.

Czech Republic and Slovak Republic

A source known in Ancient Roman times, near the village of Červenica (formerly in Hungary), produces opal as seams in grayish brown andesite rock. This opal has a mosaic of strong colors and appears very attractive against a milky white background color. Much of this is harlequin-patterned opal.

precious opal - Slovakia

Precious opal from the Slovak Republic, Slanské hills, village Červenica site – Libanka. Photo by Ivan Kopor. Licensed under CC By-SA 3.0.

Ethiopia

An ancient source of opals, Ethiopia has also had recent discoveries of precious opal in 1994 and 2008. The opal found near the town of Wegel Tena displays a remarkable play of color.

Welo opal pendant - opal gems

Diamond and gold pendant with 19.9-ct Ethiopian Welo opal. Photo by Dpulitzer. Licensed under CC By-SA 4.0.

Honduras

Deposits known since before 1843, perhaps much older than that. Occurs as veins in dark reddish to black trachyte rock. White opal contrasts strongly with the dark-colored matrix. Pieces not large, seldom very spectacular.

Indonesia

Very little known material, as thin seams in dark rock. Much of it is water opal and resembles material from Mexico. The white opal resembles poor-grade Australian. Indonesia produces some very unusual black opal that consists of reddish flecks of color swimming in a translucent but very dark brown body. Most gems are very small (less than 10 carats) from this locality, and production is very small.

Black opal - Indonesia

Black opal, Indonesia. Photo by Dharma Mulia. Public Domain.

Mexico

Mexican opal occurs in siliceous volcanic lavas, in cavities, and in many localities. Yellow and red fire opal comes from a trachyte porphyry at Zimapan in Hidalgo. Hyalite and precious opal that is completely transparent, colorless, and rich in fire occurs at San Luis Potosi. Queretaro is also a well-known opal-producing locality. Fine Mexican opal is very rare in large sizes (over 50 carats) but is among the most beautiful.

fire opal - Mexico

Fire opal, 6.3 x 5.9 x 3.3 cm, Chihuahua, Mexico. © Rob Lavinsky, www.iRocks.com. Used with permission.

Poland

Green prase opal, colored by nickel.

Tanzania

Nickeliferous opal resembling chrysoprase occurs in Tanzania, associated with brown limonite. The RI (1.452) is lower than that of chrysoprase (1.535), as is the gravity (2.125 versus 2.620). Stone sizes tend to be small.

United States

Discovered around 1900 in Virgin Valley, Humboldt County, Nevada, opal occurs here as cracks and seams in opalized wood. Magnificent but very hydrous, this opal has a strong tendency to crack due to loss of water when exposed to the air. Whole skeletons of extinct animals have been replaced by fine precious opal at this locality. Similar opal occurs in Idaho.

Spencer, Idaho has produced star opals.

Other opal sources in the United States include Arizona, Louisiana, Oregon, and Wyoming.

cushion-cut opal, Oregon - opal gems

Blue opal, 4.30 cts, Oregon, cushion cut, 10.8 x 11.2 mm. © The Gem Trader. Used with permission.

Other Opal Stone and Gem Sources

Other notable sources of opal gems include the following:

  • Bolivia; Canada; China; Myanmar; Namibia; Peru.
opal rough and cut set, Peru - opal gems

Opal rough and cut set, 3.2 x 3.2 x 2.8 cm (crystal), 12.71 cts (cabochon), Acari Mine, Caraveli Province, Arequipa Department, Peru. © Rob Lavinsky, www.iRocks.com. Used with permission.

Opal Stone Sizes

A few large and fine specimens, both opal gems and rough, have received individual names, like diamonds. Some of the most well-known pieces include the following:

  • Olympic Australis: Coober Pedy; uncut was 127 oz.
  • Noolinga Nera: Andamooka; 86 oz rough, 205-ct oval cut.
  • Roebling Opal: Nevada (Rainbow Ridge); 2,610 cts (in the Smithsonian Institution).
  • Light of the World: Lightning Ridge, Australia; 252, partly cut.
  • Red Admiral or Butterfly: Lightning Ridge, Australia; 40-50 cts rough. Many regard this as the world’s most beautiful opal.
  • Pride of Australia: Lightning Ridge, Australia; 226, partly cut.
  • Pandora: Lightning Ridge, Australia; 711, cut.
  • Smithsonian Institution (Washington, DC): Australian gems; 345, 155, 83 (all white); black opals of 58.8, 54.3, 44. Also 355 (black, Nevada); 143.2 (orange, precious, Mexico); 55.9 (colorless, precious, Mexico); 39 (pale yellow-orange, precious, Brazil).

Caring for Your Opal Stones

crazing in opal gemsOpals are delicate but well worth the extra care. They have a great sensitivity to changes in temperature as well as a “crazing” tendency, which means they can easily develop cracks or “craze” as they dehydrate. (Cracks on the surface are called “checking”).

Opals kept in water must be dried carefully before cutting.

Sometimes opals in rings can become chalk white and lifeless. This may be due to a network of scratches on the opal surface that destroys the polish and dulls the color play, but a simple re-polishing can usually correct this. Be advised that opals can be shattered or damaged beyond repair much more easily than other popular gemstones. They have a hardness of only 5.5, which makes them very susceptible to scratching. Opals aren’t recommended for ring stones, unless the stone is placed in a protective setting or a triplet or reserved for occasional wear.

Consult our care guide for opals for cleaning, setting, and storage recommendations.

Ready to learn how to identify gems on your own?

Join our mailing list below to download a FREE gem ID checklist tutorial. See what’s inside…

• Discover the 17 practical steps to gemstone identification (even if you’re just getting started with gemology)

• Learn how you can use specific tools to gather data, make observations & arrive at an accurate ID

• Explore a range of gemological tests… not only will you get familiar with the process but also time-saving shortcuts!

Free Shipping & Free Returns.

Beautiful Opal Rings, Necklaces, Bracelets & Earrings.