Onyx Stone, Properties, Facts and Photos

What is Onyx?

Onyx is a natural mineral used for a variety of purposes. In addition to gemstones, it's used for fireplace surrounds, household furniture, and ornaments.

There's a great deal of confusion surrounding the correct use of the name 'onyx.' In most cases, it's used incorrectly.

The name has been applied broadly, meaning some materials may not adhere to strict mineralogical definitions.

Regarding the colour of onyx, it's a black and white, banded variety of agate but can also be a single-coloured agate with alternating shades of light and darker-coloured bands.

Although onyx and agate are both varieties of the mineral chalcedony, the main difference is onyx has parallel bands, which are typically black and white but can also include other colours. Agate has curved or concentric bands, which can vary widely in colour and size.

What is Black Onyx?

Most black onyx being sold is either black agate or black chalcedony. Natural black onyx is quite rare.

Throughout history, the vast majority of black onyx has been dyed. In one respected gemstone reference, it's stated that in order to achieve the black colour, stones are soaked in sugar or honey before being treated with sulphuric acid.

In his encyclopedia, Naturalis Historia [circa 77-79 AD], ancient Roman author and naturalist Pliny the Elder speaks at length about techniques used to change the colour of one gemstone to make it look like another.

"There is considerable difficulty in distinguishing genuine stones from false; the more so, as there has been discovered a method of transforming genuine stones of one kind into false stones of another.

Sardonyx, for example, is imitated by cementing together three other precious stones, in such a way that no skill can detect the fraud; a black stone being used for the purpose, a white stone, and one of a vermilion colour, each of them, in its own way, a stone of high repute.

Nay, even more than this, there are books in existence, the authors of which I forbear to name, which give instructions how to stain crystal in such a way as to imitate smaragdus and other transparent stones, how to make sardonyx of sarda, and other gems in a similar manner.

Indeed, there is no kind of fraud practised, by which larger profits are made."

Ref; (Pliny's Naturalis Historia chapter 75). Please Note.

Some History of Onyx

The history of onyx can be traced back further than ancient Rome. Onyx is mentioned numerous times in the Bible and is said to have been one of the gemstones in the high priest breastplate.

This biblical garment was worn by Aaron, the first Jewish high priest, over a tunic-like garment.

Onyx is said to have been the second stone in the fourth row. To its left was a beryl, and to its right a jasper.
Much of the 'onyx' used for decorative purposes, so items like chess sets, figurines, tumbled stones and gemstones, is actually banded calcite. The stone in the image above is a perfect example.

Calcite is often used instead of onyx because it's more readily available and much softer, making it easier to work with.

According to the Traditional Birthstone Chart, ruby is the birthstone for July, but onyx can be used as an alternative.

Onyx or Calcite?

It can sometimes be difficult to tell onyx from calcite on sight alone. The simplest way to identify one from the other is to do a scratch or acid test. However, the problem with both is that some damage will be caused.

On the Mohs scale of hardness, onyx grades 6.5 to 7, calcite grades 3, therefore calcite is much easier to scratch.

To establish whether the material is calcite, you could try scratching it with fluorite or a feldspar mineral such as labradorite. Alternatively, you could use window glass or a metal knife (a regular knife used for eating). All are harder than calcite but softer than onyx.

Onyx grades 7 on the Mohs scale, so it's difficult to scratch. Quartz, which also grades 7 may scratch it, corundum, topaz, and diamond will definitely scratch it. 

An acid test will determine whether a mineral is calcite or onyx. Vinegar can also be used.

Calcite is the crystalline form of calcium carbonate. When it comes into contact with acid, it effervesces (fizzes) because of a chemical reaction between the acid and the carbonate ions in calcite. 

When acid comes into contact with calcite or another calcium carbonate mineral, tiny bubbles appear. They can be very small, so may be difficult to see. If the mineral is onyx, it will not effervesce.

Stones with light-coloured, alternating parallel bands, often sold as onyx, tend to be calcite, chalcedony, agate, or any number of other minerals.

So Much Confusion

The name onyx describes a banded variety of agate, which is a chalcedony. Chalcedony is a type of quartz that includes many different varieties.

Terminology can be ambiguous, and the translating of names into different languages, especially over hundreds or thousands of years, has further complicated matters.

In historical texts, lapis lazuli was often mistaken for sapphire because, in the ancient world, it was known as sappheiros.

Determining the exact characteristics of some minerals can be subjective and open to interpretation. Geologists often have different criteria and perspectives when defining onyx, which can lead to disagreements.

Using trade names to popularise rocks and minerals also causes confusion. Many stones that have been given a name that ends with 'Jasper' do not contain any jasper at all. An example is Dalmatian Jasper. 

Limestone onyx is a trade name for limestone that resembles onyx in appearance due to its banding but rarely has the same properties.

'Green onyx' is often agate or calcite that's been dyed.

'Onyx' or 'onyx marble' from Pakistan is travertine composed of colourful bands of calcite.

The stone in this photo, which is calcareous onyx, is a rock, not a mineral because it's an aggregate of minerals, mostly calcite or aragonite.
Calcareous onyx forms from calcium carbonate deposits, typically in caves or around hot springs. Its banding, which can be similar to true onyx, is created by layers of calcite or aragonite rather than silica.

Onyx Healing Properties

When used as a healing crystal, onyx provides strength and support, especially in difficult and stressful situations. It can help you be the master of your destiny and promotes vigour, stamina and determination.

Onyx holds onto memories so they can be used to explore past lives. It's a comforting stone for those dealing with grief and can also strengthen self-control and stimulate the power of good decision-making.

It boosts self-confidence, helps ease the fear associated with phobias, and balances yin and yang energies.

In ancient times, warriors were said to have carried onyx because they believed it would bring courage and protect them from harm. Today, it's worn or carried to protect against dark forces and promote a sense of security.

Onyx can help release negative emotions and past trauma, which allows you to heal and move forward. It promotes self-control and discipline, which can help ease addictive patterns and destructive habits.

Onyx is a stone for the present but one that carries with it happy and positive memories from the past.

Article Pictures

I'm grateful to several photographers for allowing me to use their work on our website. However, it was extremely difficult to find photos of natural onyx.

Most material labelled as 'onyx' is calcite or contains a significant percentage of calcite.

The photo at the top of our article, courtesy of Stan Celestian, is natural onyx. It's clickable and redirects to the original image.

Pop-up images: Rootbeer onyx - Courtesy of Stan Celestian. The Dalmatian Jasper tumbled stones are from our collection. Corundum, lapis lazuli - Courtesy of James St. John.  

I've linked to these next two photos of onyx because I was unable to contact the photographers to request permission to use them on our website:

https://www.mindat.org/photo-49959.html
https://www.mindat.org/photo-718344.html 

The remaining photos in our article are banded calcite. The rectangular gemstone is from our collection.

The calcareous calcite is from a social media post. Photo by Bruce Francis Taylor.