Natural stones are categorized into three geological classifications by their respective formation processes:
Sedimentary, Metamorphic and Igneous.
Each category can be either Calcareous or Siliceous.
Calcareous stone is composed mainly of calcium carbonate, a mineral compound found in stone, shells and pearls.
Siliceous stone is composed mainly of silicates, such as quartz, mica.

Stone is used for building lower layers of roads and in footpaths, parking lots, carving, etc. Crushed stone is mixed with cement and water to make concrete. Stone may be coated with bitumen to make asphalt.
Limestone is used for its alkaline properties as calcium carbonate in farming and manufacturing industry.

When heated to a high temperature limestone breaks down into lime and carbon dioxide gas, and then it is used in cement, mortar, or to improve soil in agriculture.