Onyx: Meaning, Colour, Properties & Jewellery Guide

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.

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.

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