It is an extremely hard mineral, located at the top of the hardness scale with a value of 10. Diamond is many times harder than the next hardest mineral on the scale, corundum. Although it is the hardest natural mineral, diamond has perfect cleavage in four directions. If it is struck along one of these planes, it can cleave rather easily. Rough diamonds may have a greasy appearance or adamantine luster.
Common colors are black, pale yellow, and colorless.
In the past, diamonds have been found in meteorites that have fallen to the earth. Some believe that diamond was actually contained in the meteorite while others believe that diamond forms from metamorphic processes that occur when the meteorite strikes the Earth. The name kimberlite comes from the diamond mines in Kimberly, South Africa. These kimberlite pipes are igneous intrusions and referred to as diamond pipes. Kimberlite is a common component of old continental cratons.