Sardonyx: Meaning, Symbolic Properties and Care

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Sardonyx is a banded chalcedony alternating reddish-brown bands (sard) and white bands (onyx). A stone of seals and cameos in antiquity, it is one of the August birthstones.

Key points

Colour	reddish-brown, rust, orange and white bands, sometimes black
Mineral family	banded chalcedony (microcrystalline quartz)
Simplified composition	silica SiO2; iron colours the sard reddish-brown
Mohs hardness	6.5 to 7
Origin of the name	sard (reddish-brown chalcedony) + onyx (banded chalcedony)
Historical use	seals, intaglios and carved cameos
Birthstone	August, according to the lists (with peridot and spinel)

What is sardonyx?

Sardonyx is a variety of chalcedony, the family of microcrystalline silica that also includes agate, carnelian and onyx. It is recognised by its parallel bands alternating reddish-brown to orange bands (the sard, coloured by iron) with white or black bands (the onyx). Its name combines both words: it is “sard-onyx”. Its hardness is 6.5 to 7.

The flat bands of sardonyx are like the pages of a book. This is what made it ideal for relief carving, since the carver can sculpt a white figure against a dark background.

A little history

Sardonyx has been used since antiquity. The Romans made signet rings from it, as well as intaglios (stones carved in hollow relief): hot wax does not adhere to chalcedony, which made it possible to seal documents without tearing the seal. It was also used for cameos, in which a white relief figure stands out against a brown or black ground. A famous example is the Farnese Cup, a sardonyx vessel from the 2nd century BC, held in Naples and cited as one of the largest carved gems known.

Sardonyx also appears in the Bible: in Revelation (21:20) it is the fifth foundation of the New Jerusalem. In modern birthstone lists, it is one of the August birthstones, along with peridot and spinel; these lists vary from country to country.

Traditional symbolism

In tradition, sardonyx is the stone of quiet courage, loyalty and clarity of judgement. The Romans engraved figures of gods and emperors on rings and seals. In modern use, it is credited with stability, faithfulness and commitment.

These are traditions and symbolic associations. They have no proven effect. The ancients saw it mainly as an engraving material, not as a talisman.

Traditional correspondences

Element	Association cited
Chakra	root (root chakra) and solar plexus
Element	fire and earth
Month	August
Signs	Leo and Virgo recur in many authors; this is not a rule

How to use it

As a signet ring or seal ring: the Roman tradition lives on.
As a cameo: a sardonyx cameo is a collector’s jewel.
As beads for a necklace or an earthy-looking bracelet.
As a cabochon for a pendant, or in small engraved objects.
As an August birthday gift, with the birthstone of the month.

Care

Sardonyx is hard and tolerates water well. Wash it in lukewarm water with a mild soap, rinse and dry. Avoid strong acids, which can dull its surface, and sharp knocks, which can chip its edges. Pieces whose bands have been dyed risk fading with prolonged exposure to strong light or harsh products. Finely carved cameos need a soft cloth rather than a brush. For symbolic purification: gentle smoke, moonlight; see cleansing and recharging your stones.

Treatments, imitations and confusions

Black onyx and the dark bands of sardonyx are often obtained by dyeing: agate is soaked in a sugar solution, heated, then treated with sulphuric acid; modern processes use mineral colourants based on chromium or cobalt. This treatment is old and common, but it must be disclosed.
Glass, resin or shell cameos imitate the stone: a glass cameo is perfectly regular, and bubbles may be present.
Algerian onyx, or cave onyx, is alabaster (calcite or gypsum), much softer (1.5 to 2): it is not sardonyx.
Carnelian is uniform reddish-orange, without white bands.

Reading a cameo

A cameo is read like a painting in two planes. The relief figure is carved in the white layer; the dark background is the reddish-brown layer beneath it. Look at the details: folds of clothing, hair, jewellery. An antique sardonyx cameo has fine features and subtle relief; a moulded glass or resin cameo is softer, with vague details. If you buy an antique cameo, ask for the period and the origin, and be aware that 19th-century copies are common and sometimes very beautiful.

How to choose

Look at the bands: clear, well contrasted, neatly parallel. Pieces cut as cabochons show the bands in relief; cameos must have a clean relief. The price is generally moderate, higher for antique cameos. Pair it with carnelian, onyx or agate. See also choosing and caring for your stones.