Onyx refers to a layered variety of chalcedony, a type of silicate mineral made of calcite. Onyx gemstones are usually slightly transparent or opaque, and the most commonly found type of onyx displays in two layers – a black base with a white layer on top. However, its layers can hold colours ranging from light colours to jet black. Despite the different colours and corresponding types of onyx, all forms feature multiple layers. This specific feature made onyx a favourite gem for many engraving techniques.
Natural onyx can be found and mined in a variety of countries around the world. The most dominant producers are U.S and Brazil. Other producers are, for example, Greece, China, Madagascar, Germany, the Czech Republic, the UK and others.
Many black-gem lovers may find it difficult to tell apart black onyx and black agate, as they appear similar by a quick look. Also, agate is another variety of layered chalcedony, so they are alike even on the chemical side. Luckily, there exist many differences between these two black gems.
The most noticeable difference between onyx and agate is in the form of the bands. Onyx has parallel bands, and agate has curved bands. Also, black agate shows a unique glass-like lustre – on the other hand, onyx’s lustre is more waxy-like.
As said earlier, the colour of onyx’s bands can vary from the lightest to black. We can classify onyx into various types depending on its band’s colour.
A relatively common and affordable variety of onyx is sardonyx. Sandonyx’s bands are in shades of red on a brown base.
Carnelian onyx is a variety of onyx with a red base and light colour bands on top. As with black onyx and black agate, carnelian onyx and sardonyx may sometimes be hard to tell apart.
This onyx is unique due to a thin white upper layer. This property allows the base black colour to be seen through in grey or light blue colour.
Black onyx is perhaps the most popular type of onyx due to its stunning and elegant black and white appearance. Unfortunately, natural black onyx is rarely found in nature. So most solid black onyxes found on today’s market are actually grey or black dyed chalcedonies.
Onyx has been used for jewellery and carvings for centuries. Onyx jewellery pieces are popular on the market even today thanks to their remarkable charm and exceptional durability of numbers 6.5 to 7 on the Mohs scale of hardness and affordability.
Onyx gemstone is normally cut into smooth glossy cabochons or is faceted to enhance glossiness. Onyxes can be also cut into any popular gemstone shape, such as the oval, emerald, pearl or round.