Limestone vs Dolomite
Both limestone and dolomite are types of rock made of carbonate residues. The patterns of the way they behave chemically are almost the same with varied intensities. However, the structure and the formation of these rocks are quite different.
Limestone mainly consists of two types of minerals; namely, calcite and aragonite. These are two different forms of calcium carbonate itself. The source of these calcium depositions are usually the left-over shell secretions/skeletal fragments of marine organisms such as corals. Therefore, limestone is a type of sedimentary rock formed by the deposition of material at the earth’s surface or within water bodies. Sedimentation can take place at the site of the source or at a completely different location. If it’s at a different location, these sediments are transported to the location of deposition by water, wind, ice etc.
Limestone is soluble in weak acidic media generally and sometimes even in water. Depending on the pH value of water, temperature of water, and ion concentration, calcite may remain as a precipitate or dissolve. Therefore, limestone can only barely survive in water and, when in deep water bodies, it dissolves due to high water pressure. Most ancient caves were naturally formed due to the erosion of large bodies of limestone by water over thousands of million years. Clay, silt and sand from rivers together with bits of silica (from the remains of marine organisms) and iron oxides are the most commonly found impurities in limestone. Due to the presence of these impurities in varying amounts, they exhibit different colours. Depending on the method of formation it can take different physical shapes; i.e. crystalline, granular, large rock type.
Limestone was most famous during the 19th and 20th century as many public buildings and structures were made from limestone. The Great Pyramid of Giza which is one of the Seven Wonders of the World is also made of limestone. Kingston, Ontario, Canada is nick-named the ‘Limestone City’ as many buildings are constructed from limestone. As raw material in the manufacture of cement and mortar, crushed as a solid base for roads, added as white pigment in medicines, cosmetics, toothpastes, paper, plastics etc. are among the many other uses of limestone.
Dolomite is also a carbonate mineral but is made of ‘calcium magnesium carbonate’ instead of pure calcium carbonate material. Therefore, dolomite is called a double carbonate rock, and it doesn’t readily dissolve in dilute acidic media. The way dolomite is formed is not quite clear, and it has been found that it forms under high saline conditions in environments like lagoons. Dolomite is also a sedimentary rock type. When dolomite is formed, several steps of dissolution and re-precipitation is passed where the structure of the mineral is modified into more stable forms and crystallizes in a trigonal-rhombohedral manner.
Dolomite crystals are usually white or greyish pink in colour, yet the presence of certain impurities can bring a colour change; i.e. Iron in dolomite gives it a yellowish brown tint. Furthermore, metals such as Lead and Zinc can substitute magnesium in the mineral structure. Dolomite is used as an ornamental decoration, as a source for magnesium extraction, in the making of concrete, in horticulture to add richness to the soil by balancing the pH of soil etc.
What is the difference between Limestone and Dolomite?
• Limestone is a calcium carbonate mineral whereas dolomite is made of calcium magnesium carbonate.
• Sand, clay and silt are commonly found in limestone as impurities but not quite common in dolomite.
• Calcite limestone is usually more expensive than dolomite.