The two mines in the area works a set of four kimberlite dykes. Some parts of the dykes have very high grades, and the diamonds are generally of high quality. The problem is that the mines only produce about 12 carats per 100 t.
Kimberlite is an "Igneous" rock best known for sometimes containing diamonds. It is named after the town of Kimberley South Africa, where the discovery of an 83.5-carat (16.70 g) diamond in 1871 spawned a diamond rush, eventually creating the Big Hole.