Onyx: Color, Types, Properties, Uses

Onyx

Onyx is a banded variety of chalcedony, which is a type of microcrystalline quartz. Onyx is characterized by its parallel bands of different colors. The most common color combination is black and white, but onyx can also be found in other colors, such as red, brown, and green. These bands form due to alternating layers of different mineral concentrations within the chalcedony.

Onyx has been used for centuries in various cultures, from ancient Egyptian jewelry to Roman cameos and Chinese carvings.

Onyx comes through Latin (of the same spelling), from the Ancient Greek ὄνυξ, meaning "claw" or "fingernail". Onyx with flesh-colored and white bands can sometimes resemble a fingernail.

Onyx is the traditional birthstone for July. Onyx is associated with physical and mental resilience.

Onyx is popular as a carving stone, since clever use of alternating bands of black and white can create a highly appealing carving.

Onyx is a variety or type of: Agate, which is a variety of Chalcedony, which is a variety of Quartz.

Onxy stone. Photo credit: UCL Geology Collections

Agate and onyx are both varieties of layered chalcedony that differ only in the form of the bands: agate has curved chaotic bands and onyx has parallel bands. Its multi-layered structure is similar to that of agates. When the stone has a black base and a white upper layer, it's called onyx. When the base is brown, it is called sardonyx while carnelian-onyx has a red base.

Onyx Formation

Onyx forms in cavities within volcanic rocks, with mineral-rich fluids depositing layers of chalcedony. The variations in color and pattern depend on the specific minerals present and the conditions of formation.

Onyx Types and Colors

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.

Onxy 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.

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.

Natural Onxy. Photo credit: UCL Geology Collections