According to Sangestan Mahallat, some sedimentary stones such as travertine turn into another stone when exposed to high temperature and pressure. In the process of transformation of sedimentary stones, the porous and opaque texture of these stones turns into a crystalline and polished texture and onyx stone is created.

In some cases, there are no necessary conditions for the complete transformation of travertine into onyx, and only a part of it is transformed. In such a situation Tra-onyx it happens that one part has characteristics of travertine stone and one part has characteristics of onyx stone.

Travertine is usually known for its voids, but agate lacks these voids and has a dense texture. Water absorption Tra-onyx is high in some parts and low in some parts.

Tra-onyx It is placed in the category of relatively metamorphosed limestone and sedimentary rocks, and its structure contains materials such as aragonite, calcite, and iron carbonate.Tra-onyx It is found in different colors of white, yellow, red and chocolate and is considered as a type of porous stone.

 Tra-onyx It does not take heat from the environment, that's why it always has a cold surface. Stone Tra-onyx has little resistance to cold, and if the air temperature reaches zero degrees, there is a possibility of its breaking.

 The most important mines of Tra-onyx Iran are located in the cities of Isfahan, Yazd, Kerman, Urmia, Tabriz, Zanjan and Mahallat.