According to Sangestan Mahallat, onyx is a metamorphic rock whose main mineral is calcium carbonate. The presence of aluminum and magnesium particles in onyx stones causes its color variation. Onyx stone is not suitable for exteriors because it loses its strength when exposed to sunlight and cold.

One of the properties of onyx stone is that light passes through it.

In addition to the onyx stone that is used in building architecture, there is another onyx stone that is used as jewelry. The hardness of construction onyx stone is (3) and the hardness of onyx stone used in jewelry is about (7).

Travertine stones can turn into onyx stones under high pressure and temperature and the passage of time. In general, it can be said that onyx stone is the same as baked travertine.

If the necessary environmental conditions for converting travertine to onyx are not created, or if the mine is exploited before the process of converting travertine to onyx stones is completed, the extracted product will be a stone called "Tra-onyx".

Onyx stones have very high absorption and should not be used in places with a lot of water. This stone is weaker than travertine against environmental factors such as snow, rain, and weathering, and it will break if exposed to expansion and contraction.

Onyx stone has a higher price than travertine stone, it begins to change color in front of the sun and loses its design completely in the long run. The resistance of this stone against freezing is very low.

Travertine stones have more porosity than onyx stones. Due to the presence of high porosity in travertine stones, their adhesion to mortar is very high, and it can be said that travertine stones are the best option for the exterior of the building.