Limestone is a sedimentary rock composed mostly of the skeletal fragments of marine organisms such as molluscs, coral and foraminifera. Its major minerals are aragonite and calcite which are different crystal forms of calcium carbonate.
About 10% of sedimentary rocks are limestone. Limestone is water soluble, many landscapes have been carved in limestone over millions of years. Most cave systems have been made by water going through a limestone bedrock.
In 1778 Geologist Belsazar Hacquet was the first to distinguish limestone from dolomite.
Limestone has become a very popular building material and many of the world’s best landmarks use limestone in their construction – In Egypt, The Great Pyramid has an outside covering of limestone and it’s complex in Giza is also made of limestone. Kingston in Ontario Canada has been nicknamed *the limestone city* as many of the buildings have been and continue to be made of limestone. A variety of limestone called Globigerina on the island of Malta was the only building material found on the island, and is still used frequently for the construction of sculptures and homes.
Limestone is readily available and is easy to cut into blocks for carving. It is also long lasting and stands up well to the elements, it is, unfortunately, a heavy stone which makes it impractical for tall buildings, but it is a fairly cheap building material.
In the late 19th and early 20th centuries, limestone was hugely popular and many of the banks, train stations and other buildings of that time were constructed using limestone.
During the middle ages, limestone was also a popular building block. It is a hard stone that is durable and occurs mostly on the earth’s surface and is exposed, which made it easy for people to quarry and to use. Many of the medieval churches and castles in Europe are made using limestone, and Beer Stone, which was also another popular kind of limestone that was used on medieval buildings in southern England.
Limestone and to a lesser degree marble are both reactive to acid solutions, which makes *acid rain* a problem for those wanting to preserve any artefacts made using this stone. Sadly, many building surfaces and limestone statues have suffered damage thanks to acid rain. Acid-based cleaners can also etch limestone, so care should be taken – limestone should only be cleaned with a mild alkaline or neutral based cleaner.
Other uses of limestone are wide and varied –
- Pulverised limestone is used as a soil conditioner to neutralise soils with an acidic content (agricultural lime)
- It’s the raw material used in the making of quicklime (calcium oxide), slaked lime (calcium hydroxide), cement and mortar.
- Some of the best petroleum reservoirs are geological formations of limestone
- It is crushed and used as aggregate – which is the solid base used on many roads and also in asphalt concrete
- In some cases, limestone is used in glass making
- It is added as both a cheap filler or as a white pigment in paper, plastics, toothpaste, paint, tiles and other materials
- When purified it is added to bread and cereals as a source of calcium
- Used in underground coal mines it can suppress methane explosions
- It can be used for re-mineralising and for increasing the alkalinity of purified water to restore nutrient levels and to prevent corrosion of pipes.
- It is often found in cosmetics and medicines
- When ground up it is used as a calcium supplement in feed for cattle and poultry
- It is a good material for sculptures because it is easy to carve
- Limestone binds with silica and other impurities and when used in blast furnaces it removes impurities from the iron