The category of commercial onyxes includes stones composed of layered bands of light or transparent minerals. Most onyx slabs are what geologists call banded calcite, onyx marble, Mexican onyx or Egyptian alabaster. Commercial onyx is classified as marble because it is composed of calcite, the same mineral as limestone, marble and travertine. Onyx marble is distinguished from marble by the abundance of patterns and veins. The gemstone onyx is a banded chalcedony composed mainly of silicon. On the Mohs scale, onyx gemstones have a hardness of 6-7 and onyx marble 3-4.

Onyx marble is formed in springs and underground streams where big amounts of calcite are dissolved. Beautiful crystal formations occur wherever mineral-rich groundwater flows. As the water gushes and pours around, more and more minerals are deposited, gradually forming a crust of calcite crystals. The colour differences between the layers are due to differences in the water flow and impurities. Changes in the water are reflected in the onyx layers.

The purest calcite is white or clear, but it can be easily coloured by small amounts of other minerals. The Iron oxide in the water and in the rocks give to onyx its most common yellowish-orange colour. Travertine is also formed in a similar way. The main difference between these two stones is their porosity – travertine resembles a dense sponge, while onyx is as smooth as silk, without holes.

The gemstone onyx is too expensive and is therefore used scarcely in interiors. Most often the walls and stairs are made of marble onyx which is softer than precious onyx and much more readily available. It is neither marble nor onyx, but resembles them both. Onyx marbles come in a variety of patterns and in soft, creamy colors. The most common onyx shades are green, yellow, pink and white.

One of the most attractive aesthetic properties of onyx is its ability to transmit light. Because of translucency, soft colours and bold patterns, onyx walls and counters acquire mysterious look when backlit. Artificial light sources are often installed to strengthen the effect. When combined with hidden strips of LED lights, this stone will make furniture and other elements glow.