Most diamonds come from very big and deep mines. Often the mines are in the underground ‘pipes’ of extinct volcanoes. Firstly, the top rocks are removed to make a pit. Next, huge shafts are driven beneath the pit to reach the diamonds. On the south-west coast of Africa, another type of diamond mining takes place. There, diamonds lie buried in an ancient pebble beach now covered by huge sand dunes. Over 70 million tonnes of sand and pebbles have to be removed to extract half a tonne of diamonds.
Gems like opal, topaz and emerald mostly come from very small tunnels or gravel pits close to the Earth’s surface. The earth is scooped out of the pit, washed and sieved, and any gems are hand-picked from the sieve.
Some mines are extremely deep. You can see one of the mining levels in big diamond mine. Huge pits are cut out of the solid rock so that shattered rock falls through onto railway trucks running through a tunnel. Australian opal miners actually live inside mines. It takes a lot of work to free the gems from very hard rock. People also search the rock waste dumps hoping to find opals the miners may have overlooked!
Separating diamonds
Around one gramme of diamond crystals is taken from an average of about 22 tonnes of rock — the same weight as five adult elephants. It is only because diamond has special properties that such a tiny amount can even be detected and removed.
Nearly all the diamonds that are recovered are less than 3 cm across but even 1/2 cm crystals are ‘caught’ by the grease on the conveyor belt. Diamonds can also be spotted because they glow in X-rays.
Diamonds are cleaned and sent to the sorting room, then weighed and locked up.
Picture Credit : Google