External igneous rocks (volcanic): This type of rock is also of magmatic and molten origin and has almost all the chemical properties of granite.

The difference is that in the process of rapid cooling of magma outside the earth’s crust and the release of gases, porosity occurs in the rock texture (andesite) which, when glued and embedded, absorbs the mortar well and almost integrates the rock with the mortar. . On the other hand, the specific weight of andesite stone is about two thirds of granite. This type of stone with the brand name of Sprakhon (in the northwest of the country is the name of a cold region with icy weather conditions, with severe contraction and expansion) has a special application and consumption.

Because in terms of physical and chemical characteristics and history and antiquity of use for more than a century in the famous buildings and mansions of East Azerbaijan province such as the central building of Tabriz Municipality (Clock Square) and Tabriz Bazaar and the paving of Tarbiat Street and the old Bazaar of Tabriz and various passages. Parks (Il Goli) and in the appearance of some famous mansions or recent modern buildings, is rightly known as a unique and ancient stone.

As the facade of the central building of Tabriz Municipality (Clock Square) after almost a century, with the same fall.

All the stones used in this building are andesite rock from the volcanic formation of Sahand mountain range, which has been selected and used by German experts and consultants, and after nearly a century, the smallest pores and erosion in the facade and paving stones of this The unique mansion is not observed and as the life of this building grows, its appearance becomes more impressive because this stone has the least physical, chemical and environmental passivity against erosion and is not separated from the mortar in any way.