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Limestone is all used to neutralise excess acidity – which may be caused by acid rain – in lakes and in soils. Limestone is used as a building material, and to purify iron in blast furnaces. It’s also used in the manufacture of glass, and of cement (one of the components of concrete).
Depending on the conditions under which they formed, limestone can take on a number of structural shapes, including granular (looking like mineral grains), massive (looking like an irregular blob), crystalline (looking like individual, well-formed crystals), or clastic (looking like fragments of rock). When limestones of any type undergo metamorphism, they re-crystallize as marble. Because all limestone contains calcium carbonate, which reacts with hydrochloric acid to produce bubbles, acid testing is considered one of the most reliable field tests for limestone and calcite mineral identification.