Basalt

Basalt is an aphanitic igneous rock that is relatively low in silica and alkali metals. It's usually dark grey to black in color.
Usually, basalt is used in construction, e.g. as building blocks or in the ground work, making cobblestones (from columnar basalt) and in making statues. Heating and extruding basalt yields stone wool, which has potential to be an excellent thermal insulator. Besides, basalt is a kind of raw material for the production of cast stone that is harder and more wear-resistant than alloy steel as well as more corrosion-resistant than lead and rubber. Basalt is also used as a lubricant in an advanced steel casting process, which can prolong the life of casting film. At the same time, basalt can also be extracted into glass wire that has excellent alkali resistance and high temperature resistance.