Limestone (calcium carbonate)

Limestone is a hard sedimentary rock, mainly consisting of calcium carbonate. Limestone was formed over millions of years by the deposition and sedimentation of seashells and coral, mainly made up of calcium carbonate, on the bottom of primordial oceans.

The most stable form of calcium carbonate is known as calcite. Aragonite is found much less frequently in rock (other forms such as vaterite and amorphous calcium carbonate do not play a role in the formation of limestone). Limestone almost always contains a certain quantity of impurities such as, for example, clay or sandstone. Limestone containing over 95% calcium carbonate is defined high-calcium limestone that can be converted to quicklime. The limestone quarried at Netstal is particularly pure and contains up to 98 % calcium carbonate.

When heated above 900 °C calcium carbonate decomposes to calcium oxide (CaO, burnt lime) and carbon dioxide, a chemical process known as calcination.