Diamond miners use the physical properties of the mineral to separate rough gems from common rocks and minerals. First, they concentrate diamonds and other dense particles using a technique similar to gold panning. Once they create a potentially diamond-rich concentrate, miners make use of an unusual property of diamonds for the next step in separation.
The surface of a diamond resists water, yet has an affinity for grease. This property allows mines, whether tiny one-person operations or large-scale factory-sized installations, to use surfaces coated with greasy substances to separate raw diamonds out of a concentrated ore.
Wash all of the gravel thoroughly in a bucket of water to remove any bits of leaves or sticks. Swirl the bucket to mix the gravel thoroughly and wash off loose soil and dirt.
Run the cleaned gravel through a set of graduated metal sieves to separate the material into particles of similar size. Separate the material held on each sieve into individual piles. You can sort through the largest pieces by hand.
Pour a pile from a fine sieve into a gold pan and add water. Swirl the pan continuously to separate the grains by density, pouring off the lighter material as you swirl. This action concentrates dense rock and mineral grains, including any diamonds that may be present, at the bottom of the pan.
Coat a flat or slightly concave surface with a layer of grease such as paraffin, beeswax, petroleum jelly or some mixture. Position the surface so that it is slightly tilted.
Pour concentrated ore from the pan onto the high edge of the greased surface and wash the grains gently with a stream of water. Diamonds will stick to the grease while other rock and mineral grains will wash away. Remove any grains sticking to the grease by hand and set them aside. Run the concentrate across the greased surface a second time.
Repeat the concentration and grease separation processes with the contents of the remaining sieves. Inspect the reserved grains, if any, by hand to determine whether they are diamonds.
If all the material is close to the same size, you will not need commercial sieves to separate the gravel. A handmade screen of hardware cloth may be sufficient.
Even in rich diamond deposits, a miner may find only one or two small crystals in more than a ton of gravel.