For millennia, artisans have carved intricate cameos from black-and-white onyx. Solid black onyx stones, whether faceted or cabbed, remain popular choices for striking jewelry pieces that make a bold statement.

In this detailed exploration, you'll learn:

• The unique properties of onyx stone, including its distinctive banding patterns, composition as a chalcedony variety, and what sets it apart from similar gemstones.
• The diverse varieties from classic black onyx to colorful sardonyx, along with tips to identify authentic pure onyx from common imitations.
• Practical knowledge about durability, proper care methods, and value factors to guide your jewelry purchasing decisions.
• Essential information about treatments, with most black onyx on the market being enhanced through dyeing processes that affect care requirements.
• Global sources and how different mining locations contribute to the availability and characteristics of this versatile gemstone.

What Is Onyx Stone? Understanding This Unique Gemstone

Onyx is a type of chalcedony, which is itself a form of microcrystalline quartz. Onyx stones 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. These distinctive banding patterns distinguish this stone from other gemstones and contribute significantly to its onyx meaning in jewelry design.

Is Onyx a Type of Agate? Clarifying the Relationship

When defining what makes pure onyx, there are two prevalent perspectives. Some mineralogical reference materials consider onyxes a variety of agate, suggesting the term "onyx" should specifically refer to black, brown, or white banded agates or those with monochromatic light-and-dark bands.

Other sources (including the IGS) view both agates and onyxes as banded varieties of chalcedony, distinguishing them by band orientation—agates have concentric or curved bands while onyxes display straight or nearly parallel bands, regardless of color.

In either classification system, onyx remains fundamentally a chalcedony, whether categorized as a variety or sub-variety.

Does Onyx Make a Good Jewelry Stone?

Durability Factors

Onyx stones can make exceptionally durable jewelry pieces for everyday wear. Their impressive qualities include high resistance to wear. With a hardness of 7 on the Mohs scale, onyx can effectively resist scratching from common household dust, one of the most frequent hazards during regular wear. Having no cleavage planes means onyx won't split along predictable directions when impacted. The tough tenacity of onyx allows it to resist chips and physical blows very effectively. Black variety particularly excels as a versatile gemstone that complements virtually any outfit or jewelry design.

Safety and Health Considerations

During the Victorian Grand Period (1861-1885), onyx stones gained popularity especially in mourning jewelry. Throughout centuries, this black stone has accumulated a somber and sinister body of folklore. 

Normal wearing and handling of finished onyx jewelry pose no health risks. However, gem cutters should note important precautions. Silicious mineral dust from quartz, including onyx, may cause silicosis and silicotuberculosis. Despite debates over whether non-crystalline silica causes these diseases, gem cutters should use dust masks. Proper ventilation in workspaces is essential for safety when cutting onyx. For more information, refer to our article on lapidary health hazards and safety tips.

Modern Onyx Jewelry Styles and Design Trends

Although onyx and the color black 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 diverse pieces. Contemporary designers have embraced the distinctive qualities of onyx stone. The stark appearance of black onyx creates dramatic contrast in mixed-metal settings. 

The vitreous polish luster makes onyx an excellent centerpiece stone in modern designs. Despite onyx's opacity, gem cutters often facet this material because flat surfaces can display a remarkable sheen. Black onyx pairs particularly well with silver, white gold, and platinum for striking monochromatic pieces.

Onyx Varieties: Exploring Different Types

Arabic Onyx: The Classic Black and White Stone

Although onyx 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," representing what many consider the quintessential of its appearance.

Sardonyx: The Colorful Variety

Onyx with white and reddish, brownish, or yellow layers is known as sardonyx, the traditional August birthstone. Specific varieties include distinctive variations. Cornelian or carnelian onyx has a distinctive red base color with a white upper layer. Ancient civilizations from the Near East and Europe created many remarkable sardonyx carvings. This variety demonstrates the versatility of onyx beyond the familiar black stone appearance.

Nicolo Onyx: The Blue-Appearing Variation

Nicolo onyx features a very thin layer of white color. This distinctive layer can appear almost blue against a black base color, creating a unique visual effect prized by some collectors and designers.

Black Onyx: The Most Popular Form

Pure black stones can occur naturally but with important caveats. Onyx typically forms with very thin layers of color in nature. Only rarely does it occur with layers thick enough to cut a stone as a solid color. Most solid black pieces sold today is actually dyed black chalcedony rather than naturally pure black variety. This enhancement remains standard practice in the gemstone industry.

Onyx Misnomers: Avoiding Common Confusion

The popularity of onyx has led to misuse of the term in several contexts. "Mexican onyx," "limestone onyx," or "onyx marble" is actually a type of banded calcite found in limestone caves.

Calcite is a distinct gem species, not a variety of chalcedony quartz. The optical and physical properties differ significantly—calcites have perfect cleavage and much lower hardness than onyx, making them more fragile. Other gemstones have gained "onyx" descriptions based on appearance alone. "Onyx obsidian" is simply a banded variety of natural volcanic glass. "Onyx opals" have alternating layers of common and precious opal. True onyx (chalcedony quartz), obsidian, and opal are all entirely different gem species.

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 present numerous challenges for identification. For professional testing recommendations, refer to this 1996 GIA article which offers comprehensive guidance for gemologists and collectors seeking to verify authentic onyx.

Are There Synthetic Onyx Stones? Imitations and Alternatives

Laboratories can synthesize quartz, and this material does appear in jewelry. However, consumers looking for onyx are more likely to encounter simulants—natural gemstones or lab-created materials that resemble onyx but possess distinct chemical and structural properties. black, opaque, devitrified glass is commonly used as an onyx substitute.

Black, opaque cubic zirconia may be presented as onyx in some jewelry. Natural gemstones like augite and black spinel have been offered or misidentified. Ironically, spinel represents a more durable and generally more expensive jewelry stone than genuine onyx. However, onyx has more name recognition than spinels as a black gemstone, motivating some vendors to misrepresent their products.

Even in ancient times, it inspired skillful imitations. The Roman scholar Pliny the Elder described how artisans discovered techniques to transform "genuine stones of one variety into false stones of another," assembling layers so carefully that "the artifice cannot be detected."

Do Onyx Stones Receive Gem Enhancements? Treatment Processes

Dyeing is so pervasive in the onyx market that most gem certificates note black onyx is "probably dyed". Unless a report explicitly states an onyx is free of treatments, assume enhancement has occurred. The dyeing process typically involves specific techniques. Manufacturers soak grayish chalcedony slabs in a sugar solution, then heat them in sulfuric acid. This procedure leaves tiny carbon particles in the pores of the stone.

The treatment creates black color only to a depth of a few millimeters. While generally stable, polishing heavily treated material may remove the black layer. This practice isn't recent—chalcedony's porosity has made it receptive to dyes throughout history.

Where Are Onyx Stones Found? Global Sources

This beautiful stone occurs across the globe in numerous locations. Some notable sources include:

• North America: United States, Canada
• South America: Argentina, Brazil, Uruguay
• Europe: Czech Republic, France, Germany, Scotland (United Kingdom)
• Asia: China, India, Indonesia, Yemen
• Africa: Madagascar
• Oceania: Australia
• Eurasia: Russia

Stone Sizes and Availability

Like other chalcedonies, onyx can form in substantial masses weighing several pounds and measuring many inches in diameter. This abundance contributes to onyx's relative affordability compared to other gemstones with similar aesthetic appeal.

How to Care for Onyx Stones: Maintenance Guidelines

Since onyx often receives dye treatments, proper care is essential. Clean it only with a soft brush, mild detergent, and warm water. Avoid using ultrasonic or other mechanical cleaning systems which may damage the stone. Remember that vintage and antique onyx pieces, even ancient jewelry items, may have been treated and require gentle handling. Extended exposure to strong sunlight may gradually fade dyed stones. Store separately from harder gemstones to prevent scratching. For additional recommendations, consult our gemstone jewelry cleaning guide.

Frequently Asked Questions

Is black onyx rare?

Pure black variety that occurs naturally with thick enough layers to cut as a solid color is quite rare. It typically forms with very thin layers of color in nature. This rarity is why most black pieces on the market is actually dyed chalcedony.

How can I tell if my piece is real?

Identifying real onyx can be challenging, especially when it comes to black, opaque specimens. Most gem certificates note that black piece is "probably dyed." To verify authenticity, look for uniform color, proper hardness (7 on the Mohs scale), and a vitreous polish luster. For conclusive identification, professional gemological testing is recommended.

Is it safe to wear?

Yes, wearing onyx jewelry is completely safe. Despite some historical folklore associating it with somber meanings, normal handling and wearing of finished gem pose no health risks. However, gem cutters should take precautions against silicious dust when working with raw material.

How do I care for my onyx jewelry?

Since most onyx receives dye treatments, proper care includes cleaning only with a soft brush, mild detergent, and warm water. Avoid ultrasonic or mechanical cleaning systems which may damage the stone. Keep your jewelry away from prolonged strong sunlight, which can fade dyed stones, and store separately from harder gemstones to prevent scratching.

What is sardonyx?

Sardonyx is a variety with white and reddish, brownish, or yellow layers. It's the traditional August birthstone. Cornelian or carnelian onyx, with its red base color and white upper layer, is a specific type of sardonyx that was highly prized for carvings in ancient civilizations.

What does "Mexican onyx" actually refer to?

"Mexican," "limestone," or "marble" onyx is actually a misnomer. This material is a type of banded calcite found in limestone caves, not true onyx. Calcite is a distinct gem species with different properties, including perfect cleavage and lower hardness (3) than a true one (7).