Detailed sheet


The onyx are varieties of chalcedony.
Mineralogists describe them as varieties of agate. The name comes from a Greek word meaning “nail” because of the color of the loose nail.
The gemologists and gem cutters talk about completely black gems or in banded layers of black and white colors due to be engraved or carved . They are ranked: the genuine onyx or “Arab onyx”, a black onyx or agate made of a black to very dark brown layer covered with a white layer, and almost flat, the sardonyx, with alternating white and black colors, or again brown, in which were carved famous cameos with two, three or more layers, such as the grand cameo of Sainte-Chapelle, the cameo of Vienna … The carnelian-onyx, with a red layer, used as a base, topped with a white layer, the Nicolo with a very thin top layer so that due to dispersion and transmission, the black brilliance of the underlying layer appear in bluish tones. The limestone onyx or “marble-onyx” or “onyx-marble,” is just aragonite or white calcite, yellow, brown or greenish, still zoned. It is formed by deposits of hot springs or stalactiforme concretions.



microcrystalline silica


Main color


Other colors

white, brown, grey

its black color is rarely natural

Color of streak





6.5 to 7.0


2.60 to 2.65







opaque, translucent

the slices are translucent and brown

Refractive index

1.530 - 1.540

Double refraction


very weak

visible double refraction




Number of colors





microcrystalline aggregates


Astrological sign

Aquarius, Aries, Pisces, Scorpio


It is found everywhere: USA, Turkey, Iran, Argentina, Mexico …

use in jewelry

As for the agate it is used to make ornaments, cameos, intaglios, knife handles …The onyx is the anniversary stone of the seventh year of marriage.

Daily care
and precautions

Easy to care and especially for cameos wear resistant, which is not the case of shell cameos, easy to carve but that also get damaged quickly.

imitations and

There are very few, the word onyx designated agate in white and black layers, straight or wavy but it is now recognized that this term can be applied to agates processed to become black.
We know how to make banded onyx from chalcedony, monochrome and not zoned by dipping a parallelepiped block in a solution of ammonium chloride and cobalt until it becomes black.
We then remove the stain of a millimeter thick, with hydrochloric acid , then cut the block, which gives a banded aspect with a black layer under a white layer, but the black color is not stable.
It is often imitated by artificial glasses, opaque and black.

healing properties

Talking of the onyx where black is dominant, it is considered the symbol of austerity, fear, sadness, mourning, and it would be an evil stone bringing into trouble, causing insomnia, sowing hatred and discord.
It was ascribed with terrible powers, it would cause abortion in pregnant women, making children rickety. However, if the white prevails, the onyx would be seen as a symbol of domination of light over darkness, and would own the opposite properties, giving also contemplation and wisdom while taking shelter of hysteria , epilepsy, bleeding … We recall that on the wide pectoralis that God told Moses to prepare for the high priest Aaron and adorned with twelve precious stones, the onyx is found, although the interpreters of the Bible do not all agree on the exact names of all the stones retained, it occupies the fourth row, representing Joseph.
This stone, when it is white, represents innocence, candor, sincerity being assigned to the Apostle Philip by the Christians. For the mystical exegesis, onyx is the heavenly militia of Powers. Conrad of Hamburg, German writer of the Middle Ages, in a poem, offers to the Virgin, as a memento of her wedding, a ring studded with stones, with sardonyx symbolizing its virginal gestation, the onyx all its virtues together.


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