The following uses for calcium are gathered from a number of sources as well as from anecdotal comments. I'd be delighted to receive corrections as well as additional referenced uses (please use the feedback mechanism to add uses).
- reducing agent for the preparation of metals such as thorium, uranium, zirconium, etc.
- deoxidiser, desulphurizer, or decarbonizer for various alloys
- alloys of calcium with agent for aluminium, beryllium, copper, lead, and magnesium have some useful properties
- "getter" for residual gases in vacuum tubes, etc.
- quicklime (CaO) is made by heating limestone (CaCO3) and changes into slaked lime, Ca(OH)2, on the addition of water. It is a cheap base for the chemical industry with many uses.
- calcium from limestone is a component of Portland cement. Mixed with sand it hardens as mortar and plaster while taking up carbon dioxide from the air
- the solubility of the carbonate in water containing carbon dioxide results in stalactites and stalagmites (Cheddar Gorge) and hardness in water.