Onyx Gemstone Guide

Onyx is a distinctive variety of chalcedony, which belongs to the quartz mineral family. Prized for its striking appearance and long history in jewellery and decorative arts, onyx is traditionally characterised by relatively straight, parallel bands of contrasting colours. Today, the term is most commonly associated with polished black material used in rings, pendants, earrings and other fine jewellery pieces.

This guide explains what onyx is, how it differs from similar materials, and what to consider when choosing onyx jewellery.

What Is Onyx?

Onyx is a form of chalcedony, a microcrystalline variety of quartz. Traditional onyx displays relatively straight, parallel bands of contrasting colours, often black and white. The banding is formed through the deposition of silica in layers within cavities in volcanic or sedimentary rock.

The name "onyx" is derived from the Greek word for fingernail or claw, possibly referencing the translucent, layered appearance of some specimens.

Colour and Appearance

Natural onyx may contain contrasting bands in shades of black, white, brown, red or other colours. However, much of the completely uniform black material commonly sold as black onyx has been dyed or otherwise colour-treated to achieve a consistent, deep black appearance.

Whilst naturally dark chalcedony exists, the intense, uniform black colour seen in many commercial pieces is typically the result of treatment. This does not make the material imitation, but treatments should be accurately represented where relevant.

What Is Black Onyx?

Black onyx is widely used in jewellery for its deep, polished appearance and versatility. It provides a sleek, sophisticated look that complements both modern and traditional designs.

Naturally dark chalcedony does occur, but much commercial black onyx is produced by treating lighter chalcedony to achieve a consistent black colour. Dyeing and other colour-enhancement techniques have a long history in chalcedony and onyx, and treatment is common in commercial material.

Treatment does not automatically make the material imitation, but it is important that treatments are accurately represented where relevant.

Onyx vs Agate

Both onyx and agate are forms of banded chalcedony, but they differ in the pattern of their banding. Onyx traditionally has relatively straight, parallel bands, whilst agate more commonly displays curved, irregular or concentric banding.

In practice, the terms are sometimes used interchangeably in the trade, particularly for dyed or treated material. However, the distinction lies in the banding pattern rather than colour alone.

Durability and Hardness

Onyx has a Mohs hardness of approximately 6.5–7, making it suitable for many types of jewellery, including:

• Rings and signet rings
• Earrings
• Necklaces
• Pendants
• Bracelets
• Cufflinks

Whilst onyx is reasonably durable, it can still scratch, chip or fracture if subjected to hard impacts or abrasion from harder materials. Care should be taken when wearing onyx jewellery during activities that may expose it to knocks or rough surfaces.

Where Is Onyx Found?

Onyx and chalcedony materials are found in various locations around the world. Recognised producing regions include Brazil, India, Madagascar, Uruguay and other locations.

Geographic origin alone does not determine quality. The appearance, colour, banding, polish and overall finish are more important factors when assessing onyx.

Assessing Onyx Quality

When considering onyx jewellery, customers may assess the following factors:

• Colour: Depth, uniformity and appeal of the colour
• Banding: Presence, pattern and contrast of bands where present
• Uniformity: Consistency of colour and appearance
• Surface quality: Smoothness and freedom from visible flaws
• Cut: Shape and proportions of the finished piece
• Polish: Quality and lustre of the polished surface
• Treatments: Whether the material has been dyed or otherwise treated
• Overall appearance: How the piece looks when worn or displayed

Natural and Treated Onyx

Dyeing and other colour-enhancement techniques have a long history in chalcedony and onyx. Treatment is common in commercial material, particularly for achieving the uniform black colour associated with black onyx.

Not every piece of black onyx is treated, but treatment is widespread. Reputable jewellers should accurately represent the treatment status of their onyx pieces where relevant.

Onyx vs Obsidian

Onyx and obsidian can both appear black and glossy, but they are completely different materials.

Onyx is chalcedony within the quartz family, formed through the deposition of silica in layers. Obsidian, on the other hand, is natural volcanic glass formed when lava cools rapidly. Obsidian is typically more brittle and has a different internal structure to onyx.

Caring for Onyx Jewellery

To keep onyx jewellery looking its best, follow these care recommendations:

• Clean onyx jewellery with lukewarm water, mild soap and a soft cloth or soft brush
• Rinse thoroughly and dry with a soft, lint-free cloth
• Avoid harsh chemicals, abrasive cleaners and rough handling
• Avoid hard impacts and extreme heat
• Avoid prolonged exposure to chemicals that could affect dyed or treated material
• Avoid ultrasonic or steam cleaning when the treatment history is unknown
• Store onyx jewellery separately from harder gemstones that may scratch its polished surface

Onyx Meaning and Symbolism

Throughout history, onyx has been associated with various symbolic meanings, including strength, protection, confidence and self-control. In some traditions, it has been regarded as a grounding stone that promotes focus and resilience.

These associations are cultural and symbolic in nature. No gemstone, including onyx, has proven healing, medical or supernatural properties.

Is Onyx a Birthstone?

Onyx is not one of the principal modern monthly birthstones recognised by major gemmological organisations. However, it has appeared in some historical and alternative birthstone traditions, and is sometimes associated with the zodiac sign Leo.

Birthstone traditions vary by region and culture, and personal preference is always the most important factor when choosing jewellery.

Conclusion

Onyx is a distinctive variety of chalcedony within the quartz family, traditionally characterised by straight, parallel banding and now most commonly associated with polished black material. With a Mohs hardness of approximately 6.5–7, onyx is suitable for a wide range of jewellery applications, from rings and signet rings to earrings, necklaces and bracelets.

Whilst naturally dark chalcedony exists, much commercial black onyx is treated to achieve a uniform black colour. Treatment is common and does not make the material imitation, but it should be accurately represented where relevant.

Whether you are drawn to onyx for its sleek, sophisticated appearance, its long history in jewellery, or its symbolic associations with strength and confidence, understanding its composition, durability and care requirements will help you choose and maintain onyx jewellery that you can enjoy for years to come.