Sardonyx

Sardonyx is a geological oddity of a stone – essentially, it is Sard mixed with Onyx. The red Sard creates an interesting contrast between the white or black Onyx.

Sardonyx has been used since antiquity for various things, including seals and cameos and other decorative objects made by the Assyrians, Romans, Greeks and Phoenicians. It is a perfect stone for carving hard cameos, as it has very contrasting layers.

Showing all 1 result

Appearance, Uses and History

There is a huge amount of confusion around what Sardonyx actually is.

Sard is a brown to brownish red, transparent to translucent variety of Chalcedony.
Onyx is a form of Chalcedony, sometimes used to describe solid black or banded black and white Chalcedony.
Agate is a multi coloured banded form of Chalcedony.
Chalcedony is a microcrystalline variety of Quartz, and occurs in many varieties.
Carnelian is a dull red variety of Chalcedony.
Sardonyx, specifically, is a mixture of Sard and Onyx, consisting of parallel bands of brown, white, and red, sometimes with black bands. It could be considered an Onyx or an Agate depending on specific definition.

This material has been mined or gathered since around 2200BCE; throughout most of recorded history it has been used as lapidary material for bas-relief art; otherwise known as ‘low relief’.

This is a technique in which the design and details are barely more prominent than the overly flat background. In this case, Sardonyx is carved so that the background layer is a different colour to the details.

It is used for hardstone cameos, which are harder wearing than shell based cameos. It was a popular material for making seals and signet rings, as apparently hot wax does not stick to the stone.


Locales

The best source for contrasting Sardonyx is India, although there are deposits from Brazil, Germany, Madagascar and the USA.


Mineralogy

Chemistry
A variety of crypto-crystalline Quartz, SiO2.
Colours and Variations
Bands of white, black, brown, red-brown and red.
Streak
White
Luster
Waxy
Fracture
Conchoidal
Transparency
Translucent or opaque
Crystal habit
Fibrous to grained aggregate.
Mohs hardness
6.5 – 7.0
Specific Gravity
2.55 – 2.70
Easiest testing method
Common Treatments
Heating and dyeing have been known – especially dyeing.

Photos of Sardonyx

AlexanderCameo
Cameo enthroned prince Louvre MR80

Cameo Athena CdM Babelon17
Prince ptolémaïque assimilé à Hermès CDM camée 111
Cameo Messalina Cdm Paris Chab228

Hazards and Warnings

Almost all rocks, minerals (and, frankly, almost all other substances on earth) can produce toxic dust when cutting, which can cause serious respiratory conditions including silicosis.

When cutting or polishing rocks, minerals, shells, etc, all work should be done wet to minimise the dust, and a suitable respirator or extraction system should be used.


Translations

Arabic:

  • الجزع العقيقي

Hindi:

  • गोमेदक

Portuguese:

  • sardônica
  • sardônico

Bengali:

Indonesian:

Punjabi:

English:

Italian:

  • sardonica

Russian:

  • сардоникс

French:

Japanese:

  • サードニクス

Spanish:

German:

Korean:

  • 사도 닉스

Thai:

Gujurati:

Mandarin and Traditional Chinese:

  • 缠丝玛瑙
  • 纏絲瑪瑙

Urdu:


Further Reading / External Links