Onyx Value, Price, and Jewelry Information

Pear-cut black onyx set in a delicate gold engagement ring with skull accents. © CustomMade. Used with permission.

Onyx

For millennia, artisans have carved intricate cameos from black-and-white onyx. Solid black onyxes, faceted or cabbed, are also popular jewelry stones.

Onyx Information

Data Value
Name Onyx
Is a Variety of Chalcedony
Varieties Sardonyx
Colors Black, white (banded). Varieties may show red, brown, yellow, and blue layers. Solid black onyx may also occur, though most such specimens are dyed.
Crystallography Hexagonal (trigonal), microcrystalline
Refractive Index 1.544-1.553
Luster Waxy
Polish Luster Vitreous
Hardness 7
Wearability Excellent
Fracture Conchoidal
Specific Gravity 2.651
Birefringence 0.009
Cleavage None
Dispersion None
Heat Sensitivity No
Enhancements Dyeing, heating (common)
Typical Treatments Dyeing, Heat Treatment
Transparency Opaque
Formula

SiO2

Pleochroism

None

Optics

Uniaxial (+)

Optic Sign Uniaxial +
Etymology

From the Greek word for “fingernail” or “claw.”

Occurrence

Can occur in a wide variety of mineral environments.

Onyx stone

Onyx, photo by Simon Eugster. Licensed under CC By-SA 3.0.

Comments

Onyx is a type of chalcedony, which is itself a form of microcrystalline quartz. Onyxes have straight, nearly parallel bands or layers of color, which allow skilled gem carvers to cut away material to create cameos and intaglios with extraordinary depth and contrast.

Venus Marina, onyx cameo, 19th century

Benedetto Pistrucci’s “Venus Marina, Cupid at Her Side,” onyx cameo in a gold frame (5.7 x 4.4 cm), London, ca. 1820-1830. The Milton Weil Collection, 1940. Metropolitan Museum of Art, New York. Public Domain. (Cropped to show detail).

Arabic Onyx

Although onyxes may occur with bands of various colors, white and black layers are the most familiar. Gems with a black base color and a white upper layer are known as “true” or “Arabic onyx.”

brooch and earrings with onyx cameos - Arabic onyx

Yellow gold brooch and earrings with onyx cameos, featuring classic black base colors and white upper layers. Photo courtesy of liveauctioneers.com and Leighton Galleries.

Sardonyx

Onyx with white and reddish, brownish, or yellow layers is known as sardonyx, the traditional August birthstone. Cornelian or carnelian onyx has a red base color and a white upper layer. Ancient civilizations from the Near East and Europe created many amazing sardonyx carvings.

sardonyx cameo of Emperor Augustus - Roman, onyx

Sardonyx cameo in a gold frame of the Emperor Augustus on the horns of a double-headed goat (2.8 cm), Roman, 27 BCE-14 CE. Gift of Milton Weil, 1929. Metropolitan Museum of Art, New York. Public Domain.

Nicolo Onyx

Onyx with a very thin layer of white, which can appear almost blue against a black base color.

nicolo onyx - Roman

Nicolo onyx gemstone (1.3 x 0.4 cm), Roman, 2nd-4th century CE. Rogers Fund, 1922. Metropolitan Museum of Art, New York. Public Domain.

Black Onyx

Onyxes usually form with very thin layers of color. Although, very rarely, they can occur in nature with layers thick enough to cut a stone as a solid color, most solid black onyxes sold today are actually dyed black chalcedonies.

Onyx Jewelry

During the Victorian Grand Period (1861-1885), onyxes were popular gemstones, especially for mourning jewelry. Over the centuries, these stones have accumulated a somber and sinister body of folklore.

Victorian onyx and marcasite mourning jewelry

This 14k yellow gold Victorian mourning brooch features a 2” polished onyx oval and marcasites set in a silver floral crest. Photo courtesy of liveauctioneers.com and GWS Auctions Inc.

Although onyx and the color black in general still carry funereal associations in Western cultures, jewelry styles since Victorian times have utilized onyx’s dark and opaque appearance to complement transparent colored gems as well as diamonds in a variety of pieces.

Art Deco onyx and diamond platinum brooch

This Art Deco platinum bow brooch (ca. 1930) features 16 rectangular and trapezoidal faceted black onyxes and 46 round, old European-cut diamonds. Photo courtesy of liveauctioneers.com and Quinn’s Auction Galleries – Central Virginia.

Contemporary jewelers have also seized on the stark appearance and vitreous polish luster of onyxes to make them center stones in their own right. Despite onyx’s opacity, gem cutters will often facet this material because the flat surfaces can show a remarkable sheen.

oval-cut black onyx statement ring

Bold, nature-inspired statement ring featuring an oval-cut black onyx. © CustomMade. Used with permission.

Is Onyx a Type of Agate?

Some mineralogical reference materials consider onyxes a variety of agate, itself a variety of chalcedony. According to these sources, the term “onyx” should refer to black, brown, or white banded agates or those with monochromatic light-and-dark bands.

Alternatively, other sources (including the IGS) consider agates and onyxes both banded varieties of chalcedony, only agates have concentric or curved bands and onyxes straight or nearly parallel bands. These distinctions hold regardless of the color of the bands or layers.

Of course, in either case, onyx remains a chalcedony, whether as a variety or sub-variety.

onyx eye on crystalline quartz - Brazil

If onyx is a variety of agate, then this specimen certainly qualifies. The striking black-and-white bullseye-like layer of chalcedony actually grew on a matrix of terminated crystalline quartz. 7.0 x 5.8 x 5.5 cm, Minas Gerais, Southeast Region, Brazil. © Rob Lavinsky, www.iRocks.com. Used with permission.

Onyx Misnomers

The popularity of onyx, however, had led to some misuse of the term. The most common example of this is so-called “Mexican onyx,” “limestone onyx,” or “onyx marble.” This material is actually a type of banded calcite found in limestone caves.

Calcite is a distinct gem species, not a variety of chalcedony quartz. They have different optical and physical properties. Notably, calcites have perfect cleavage and a much lower hardness than onyxes, thus making them much more fragile. Artisans have used this banded calcite material for millennia to carve decorative items. Today, consumers can still find many objects for sale labelled as “onyx marble.” Although this remains a widely used term, keep in mind that this material isn’t onyx at all.

"onyx marble" vessel - Mexico

This vessel in the shape of a monkey was carved from “onyx marble,” known as tecali to the Mixtec Meso-Americans. It also sports pyrite eyes and shell teeth. 19.1 x 12.7 x14 cm, Mexico, 10th-12th century CE. The Michael C. Rockefeller Memorial Collection, Bequest of Nelson A. Rockefeller, 1979. Metropolitan Museum of Art, New York. Public Domain.

Other gemstones have gained “onyx” descriptions based on their appearance, too. For example “onyx obsidian” is a banded variety of that natural glass. “Onyx opals” have alternating layers of common and precious opal. Of course, quartz (onyx), obsidian, and opal are all distinct gem species.

Identifying Characteristics

Black, opaque gemstones pose numerous challenges for identification. This 1996 GIA article offers some testing recommendations.

engagement ring with black onyx and yellow sapphires

This daisy-inspired engagement ring features a black onyx in an 8-claw prong setting and bezel-set yellow sapphires. © CustomMade. Used with permission.

Synthetics

Laboratories can synthesize quartz, and this material does appear in jewelry. However, consumers looking for onyxes are more likely to encounter simulants, natural gemstones or lab-created materials that look like onyxes but with distinct chemistry and/or crystal structures. 

For example, synthetic materials such as black, opaque, devitrified glass as well as black, opaque cubic zirconia have been used as onyx substitutes. Natural gemstones such as augite and opaque, black spinel have also been offered or misidentified as onyxes. Oddly enough, spinel makes a more durable and generally more expensive jewelry stone than onyx. However, as a black gemstone, onyx has more name recognition than spinel, so that may motivate some vendors to sell black spinels as onyxes.

Even in ancient times, onyxes inspired some skillful imitations. For example, the Roman scholar Pliny the Elder described how some “have discovered how to make genuine stones of one variety into false stones of another.” For example, so-called sardonyxes were assembled from layers of black, white, and vermillion stones so carefully that “the artifice cannot be detected.”

Enhancements

Dyeing onyxes isn’t a recent development, nor is it limited to solid black specimens. Since these gems may have very thin color layers, dyes may be used to enhance them. Chalcedony is extremely porous, so it readily absorbs dyes of any color.

sardonyx cameo - Italian, onyx

Carving cameos in onyxes to just the right depth to reach desired colors is very challenging, especially when the stones have very thin color layers. In this sardonyx cameo from the 18th century, the carver cut through the red layer on some of the lion’s tail and rear leg. Although not the case in this piece, dyes could be used to match the color of exposed areas to the desired layer. 17.1 x 25.5 mm, Italian. The Milton Weil Collection, 1939. Metropolitan Museum of Art, New York. Public Domain. (Cropped to show detail).

To create black onyxes, manufacturers typically soak grayish slabs of chalcedony in a sugar solution, then heat them in sulfuric acid. However, this procedure may leave tiny carbon particles in the pores and creates black color only to a depth of a few millimeters. Although this is a stable process, polishing such treated material may remove the black layer.

Dyeing is so pervasive that most gem certificates will note that black onyxes are “probably dyed.” Unless a report explicitly states a black onyx is free of treatments, assume it’s treated.

dyed, vintage black onyx spacer beads

Vintage spacer beads, custom-cut black onyxes. Note the gray color in the bead holes and some surface areas. Like most black onyxes, these stones were dyed. Photo © Joel E. Arem, PhD, FGA. Used with permission.

Sources

Onyxes occur across the globe. Some notable sources include the following locations:

  • Argentina; Australia; Brazil; Canada; China; Czech Republic; France; Germany; India; Indonesia; Madagascar; Russia; Scotland, United Kingdom; United States; Uruguay; Yemen.

Stone Sizes

Like other chalcedonies, onyxes can form in masses several pounds in weight and many inches in diameter.

Care

Onyxes can make durable jewelry stones. Their hardness of 7 means they can resist scratching from one of the most common hazards of everyday wear: household dust. With no cleavage and a tough tenacity, they can resist chips and physical blows well.

Gem cutters should note that silicious mineral dust from quartz, including onyxes, may cause silicosis and silicotuberculosis. Although some debate exists over whether non-crystalline silica will cause these diseases, gem cutters should still use dust masks and have proper ventilation for their workspaces. See our article on lapidary health hazards and safety tips for more information. Wearing and handling finished stones should pose no risks.

Since onyxes often receive dye treatments, clean them only with a soft brush, mild detergent, and warm water. Don’t use ultrasonic or other mechanical cleaning systems. Keep in mind that vintage and antique onyxes as well as ancient jewelry pieces may have been treated, too.

Consult our gemstone jewelry cleaning guide for more care recommendations.

modern black onyx ring

A modern, asymmetric onyx ring, inspired by space/galaxies/stars. © CustomMade. Used with permission.