Onyx, in strict gemological terms, is a variety of chalcedony characterized by straight, parallel bands of contrasting colors, typically black and white. In modern trade, the term 'onyx' is often used more loosely for solid black chalcedony, much of which is dyed. With Mohs hardness around 6.5–7 and good toughness, onyx is suitable for intaglios, cameos, cabochons and beads.
Price History
Value Drivers
Carat weight is secondary; onyx is abundant and readily available in large pieces. Larger cameos, signet stones and carvings may be more valuable due to labor and design, but price per carat remains modest except for finely carved or antique pieces.
Color and banding are primary value factors. In banded onyx, sharp, straight layers of black and white that can be exploited for cameos are desirable. For solid black onyx, a deep, uniform black with high polish and no brown or gray undertones is preferred. Many black onyx stones are dyed to enhance color.
Onyx is opaque; clarity focuses on structural integrity and surface quality. Compact material free of cracks, pits and significant inclusions is preferred for carving and setting. Surface-reaching fractures or large porous zones lower durability and value.
Onyx is commonly cut as cabochons, beads, cameos and intaglios. Good cutting emphasizes symmetry, proportional domes and a smooth, high polish. For banded material, cutters position layers strategically to create contrast in carved designs.
Market Dynamics
Chalcedony deposits suitable for onyx occur in many countries, including Brazil, Uruguay, India and others. Black chalcedony is abundant, and dyeing expands the supply of black onyx-like material even further, ensuring ample availability for jewelry markets.
Demand is consistent in men's and women's fashion jewelry, signet rings and rosaries, as well as in decorative carvings. Onyx remains a staple gem for bold, monochrome designs and is widely used in silver and gold jewelry.
Recent Trends: steady demand from the broader jewelry market, with gradual growth in online and designer channels for well-cut, natural stones.
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Insights
Historically, onyx was prized for cameos and intaglios, where carvers exploited the color contrast between layers.
Much of the 'black onyx' in modern jewelry is dyed chalcedony; natural un-dyed black chalcedony is less common.
Onyx's relative hardness and toughness make it suitable for rings and cufflinks, though polished surfaces can show wear over time.
Onyx has been used in decorative architecture, inlay and mosaics for centuries.
Testing can distinguish natural from dyed material through color concentrations in fractures and reactions to certain solvents.
Onyx's affordability means that design and branding are often the main drivers of finished jewelry prices.