Onyx
Onyx is a variety of chalcedony in the quartz family. In its precise gemological sense, the name refers to chalcedony with straight, parallel black and white layers. In jewellery, “black onyx” is also used for uniformly black chalcedony, whose smooth appearance and deep colour give a piece a quiet, distinct presence.
Gemological Properties
| Property | Information |
|---|---|
| Mineral family | Quartz — chalcedony |
| Main chemical composition | SiO₂ — silicon dioxide |
| Structure | A dense aggregate of minute crystals, commonly with a fibrous structure |
| Hardness | Approximately 6.5–7 on the Mohs scale |
| Specific gravity | Typically approximately 2.58–2.64 |
| Refractive index | Typically approximately 1.53–1.54 as a spot reading |
| Colour | Black and white in layers; uniformly black material is also sold in the trade |
| Transparency | Translucent to opaque; black onyx generally appears opaque |
| Lustre | Waxy to vitreous, depending on the polish |
These values refer to chalcedony onyx. A stone’s composition and condition may affect its measurements.
Layering and the Black Appearance
In layered onyx, the contrast between black and white can be used for carvings: a pale figure standing above a dark background, or an engraving extending from one layer into another. This is one reason for the historical use of onyx in amulets, seals and carved jewellery.
Uniformly black onyx is often cut as a cabochon, emphasising its colour and smooth surface.
White Onyx
In the jewellery trade, “white onyx” is also used for white chalcedony with a milky appearance, either uniform or subtly layered. This is a broader commercial usage than the precise gemological definition of onyx with black and white layers. It should be distinguished from white calcite, which is also sometimes sold as “white onyx” but is a different material with different properties.
Natural Colour and Treatments
Much of the black chalcedony sold as “onyx” is treated to produce its black colour. The base material can be natural even when its colour has been obtained through treatment.
It is therefore important to distinguish the origin of the material from the origin of its colour: “natural stone” does not necessarily mean untreated natural colour.
Sources Around the World
Chalcedony and agate, including material used commercially for black onyx after treatment, come from countries including Brazil and Uruguay. Onyx with a striking contrast between black and white layers has also been documented in the Gao region of Mali.
The place where the rough was mined should be distinguished from the place where it was dyed, cut or carved.
Cleaning and Care
Clean gently with a soft, damp cloth and, when needed, lukewarm water with a little mild soap. Rinse and dry afterwards.
Avoid extreme heat, sudden temperature changes and contact with substances that could be absorbed by the stone or alter its appearance. When its treatment history is unknown, gentle hand cleaning is preferable.
Spiritual Meaning
Onyx is associated with inner strength, perseverance and self-control. It symbolises the ability to remain focused over a long journey, act with discipline and finish what we have started. It can serve as a reminder to direct willpower towards personal growth and consistent action.
Spiritually, it is also associated with grounding, stability and gathering strength within. It symbolises considered reflection, attention to detail and maintaining personal boundaries, alongside the ability to combine inner listening with practical action in everyday life.
These meanings belong to the realm of belief and symbolism. They can give jewellery personal significance, but they are not proven gemological properties or a promise of healing, protection or a change in health.