Diamonds are believed to have been formed deep within the earth by great heat and pressure. They are forced to the surface with molten rock during various types of eruptions. Molten rocks solidify into kimberlites thereby forming pipes. Pipes are tubular in shape and extend to great depths. The open-pit method is used to mine pipes to a depth of several hundred feet. A pound of diamonds on the average is obtained after processing about 20 million pounds of rock.
There are however secondary sources of diamonds which are deposited by running water. This is what is referred to as alluvial deposits which are formed when relatively soft kimberlite is eroded by water. The diamonds are carried away by water and are deposited in stream beds or on stream banks.
Diamonds are extracted from the ore by crushing the ore and mixing it with water to form a dense mud. The mixture is stirred in a large circular pan to cause the lighter materials to rise and the heavier materials including the diamonds to sink to the bottom. Diamonds are completely separated from the other materials through grease tables or electrostatic charge.
