Limestone

limestone, a rock made of the mineral calcite (calcium carbonate); dolomitic limestone or dolomite is a mixture of calcium-magnesium carbonate. Limestone is calcaire in French.

Common limestones differ from chalk (a soft form of limestone) in being hard and not readily penetrated by plant roots, except through cracks. Unless mineral material is brought in by wind or water, the depth of soil formed on limestone depends on the impurities (clay, silt, and sand) in the limestone because the dissolution of calcite produces only calcium and bicarbonate ions. Some limestone soils, such as the Mediterranean terra rossa, are red-brown in colour; these are moderately alkaline and have a good clay-loam texture and structure.