Black Onyx Guide

Onyx is microcrystalline quartz (chalcedony) with parallel colour bands. Natural pure black onyx is uncommon, so most jewellery onyx is chalcedony dyed black. The dye is stable. Sardonyx alternates red-brown sard layers with white, and has been used for cameos for thousands of years.

Solid black with a smooth, mirror-like polish is the most common form. Natural banded onyx shows alternating layers of black and white. Sardonyx shows red-brown and white. Green and blue onyx are dyed and less traditional.

Onyx is 6.5 to 7 on the Mohs scale with good toughness. Suitable for rings, signets, cufflinks, earrings and pendants. The dye can be affected by aggressive chemicals or prolonged sunlight, so onyx asks for gentler care than a sapphire or ruby.

For dyed black onyx, evenness of colour and quality of polish matter most. For banded onyx and sardonyx, the sharpness and contrast of the bands. Cameos and intaglios are judged on carving quality as much as the material.

Most onyx in fine jewellery is dyed chalcedony. The dyeing process is ancient and stable. Brazil, India, Madagascar, Uruguay and the USA all supply the market. India is the largest processor.

Signet rings, cocktail rings, men's wedding bands, cufflinks and Art Deco-style pieces. Onyx pairs beautifully with diamonds and white metal for high-contrast designs. Onyx bead bracelets and necklaces are also popular.

Clean with warm soapy water and a soft cloth. Avoid ultrasonic and steam cleaners because they can affect dyed material. Protect from harsh chemicals, acids and prolonged direct sunlight. Store separately.

Black onyx is one of the most affordable gemstones. Cameos and antique sardonyx pieces are valued for carving and provenance more than for the material itself.