Appearance
Calcium is a silvery white, relatively soft metal

Source
Calcium is the fifth most abundant metal in the Earth's crust, greater than 3% by mass. It is not found free in nature, but occurs in large amounts as Limestone (Calcium carbonate), Gypsum (Calcium sulphate), Fluorite (Calcium fluoride) and Apatite (Calcium chloro- or fluoro-phosphate). Calcium is prepared commercially by the electrolysis of fused Calcium chloride to which Calcium fluoride is added to lower the melting point.

Uses
Calcium oxide (Quicklime), which is made by heating Limestone and which can be changed into Slaked Lime by the addition of water, is widely used in the chemical industry. It is cheap and readily available. When mixed with sand it takes up Carbon dioxide from the air to form mortar and plaster. Calcium from Limestone is an important part of Portland Cement. Calcium is also used as a reducing agent in preparing other metals such as Uranium and Thorium, and as an alloying agent for Aluminium, Beryllium, Copper, Lead and Magnesium alloy.

General Information
Calcium is an essential constituent of cells, teeth and bones. The normal amount in an average adult exceeds 4kg, and is located mainly in the teeth and bones.

Calcium readily forms a white coating of nitride in air, it reacts with water and burns with a yellowish red flame, forming mostly the nitride. Calcium carbonate is soluble in water containing Carbon dioxide, and this causes hardness in water. Calcium carbonate dissolved in water also forms stalagmites and stalagtites in caves.