Onyx: Color, Types, Properties, Uses

First, what is onyx? Onyx is a stunning natural stone, celebrated for its mesmerizing translucence and classic sophistication.

Onyx is a banded variety of chalcedony, which itself is a microcrystalline form of quartz (SiO₂). What distinguishes onyx is its parallel bands of contrasting colors, most commonly black and white, though red, brown, and green varieties also occur. These bands form through rhythmic silica deposition in cavities, often influenced by changes in mineral content and fluid chemistry during formation.

The name “onyx” comes from the Latin onyx, derived from Ancient Greek ὄνυξ (ónux), meaning "claw" or "fingernail"—a reference to the flesh-toned and white-banded varieties that can resemble a human nail.

Historically, onyx has been valued across many cultures: from ancient Egyptian amulets and Roman cameos to Chinese carvings. It is prized for its aesthetic appeal and is widely used in jewelry and ornamental carvings, where artisans often exploit the contrasting layers for visual effect.

Onyx is sometimes confused with agate, as both are banded varieties of chalcedony, a microcrystalline form of quartz. The key difference lies in the banding pattern: onyx exhibits straight, parallel bands, while agate features curved or irregular (often concentric) bands.

Both stones are formed by the rhythmic deposition of silica-rich fluids in cavities within volcanic rocks, producing a layered structure. The variation in band color results from differences in mineral impurities and formation conditions.

Onyx typically has a black base with a white upper layer. When the base is brown, the stone is called sardonyx, and when it has a red base, it may be referred to as carnelian-onyx. These names are based on the color of the underlying layers in the stone's structure.

Onyx Color

Onyx isn’t an actual family of gemstones, rather a term used to describe layered stones that contain bands of black and white.

Black Onyx

Black Onyx The most common and popular type of onyx, exhibits deep black bands, often with white or gray streaks. Black Onyx formed by alternating bands of black chalcedony and white quartz or calcite.It is widely used in jewelry and ornamental objects due to its elegant and timeless appeal.

White Onyx

This variant showcases bands of white, often with a translucent appearance. White onyx is cherished for its purity and is commonly used in carvings and sculptures.

Green Onyx

Characterized by captivating green bands, this type of onyx exudes a sense of tranquility. It is popular in jewelry and decorative pieces.

Red Onyx

With vibrant red bands, red onyx is a rare and luxurious variation. It is frequently used in high-end jewelry and unique interior designs.

Sardonyx

Sardonyx is a variety of onyx that exhibits bands of brownish-red (sard) and white or black. It is highly prized for its distinctive appearance and is frequently used in cameos and intaglios.

Onyx agate with Quartz from Uruguay, at the Mineralogy Gallery in Paris.
Photo: Camille Gévaudan

Artificial treatments have been used since ancient times to produce both the black color in "black onyx" and the reds and yellows in sardonyx. Most "black onyx" on the market is artificially colored.

Onyx is a gemstone found in various regions of the world including Greece, Yemen, Uruguay, Argentina, Australia, Brazil, Canada, China, Czech Republic, Germany, Pakistan, India, Indonesia, Madagascar, Latin America, the UK, and various states in the US.

Onyx from Brazil.
Photo: James St. John

Onyx Properties

Crystal System: Trigonal
Color: Various
Cleavage: no cleavage
Fracture: Onyx has a conchoidal fracture, which means that it breaks into smooth, curved surfaces that resemble the inside of a seashell.
Mohs scale hardness: 6.5–7
Luster: Vitreous, silky
Streak: White
Specific gravity: 2.55–2.70 g/cm³

Uses of Onyx

Onyx, with its distinctive banded beauty and versatile properties, finds its way into a wide range of uses, from adorning your finger to gracing your home décor. Here's a glimpse into the diverse world of onyx applications:

Onyx agate from Minas Gerais, Southeast Region, Brazil

Jewelry and Decorative Objects:

Earrings, necklaces, bracelets, and rings: Onyx's beauty and durability make it a popular choice for jewelry. Its layered patterns add visual interest, and its hardness allows for intricate carvings and polishing.
Cameos and Intaglios: The contrasting colors of onyx layers make it ideal for creating cameos (raised carvings) and intaglios (engraved designs). These techniques were popular in ancient civilizations and are still appreciated for their artistic value.
Sculptures and decorative objects: Onyx's ability to take a high polish and its unique banding patterns make it suitable for crafting sculptures, vases, bowls, and other decorative items.

Practical Applications:

Ancient amulets and talismans: Many cultures, including ancient Egyptians, Greeks, and Romans, believed onyx possessed protective properties. They used it to craft amulets and talismans to ward off evil and bring good luck.
Mortars and pestles: Onyx's hardness and non-porosity make it ideal for grinding spices and herbs.
Architectural elements: Onyx slabs have been used for flooring, countertops, and other decorative elements in buildings. Its durability and unique appearance make it a striking addition to any space.

Onyx stone.

Metaphysical and Healing Properties

In crystal healing, onyx is associated with grounding, protection, and self-control. It is believed to help absorb negative energy and promote emotional stability.