Two different minerals are formed from the element carbon. One is graphite which is one of the softest minerals on Earth. The other is diamond which is the hardest substance on Earth (10 on Mohs' hardness scale). The difference in hardness is due to the way the carbon atoms attach to one another. In diamond, they attach in a three-dimensional manner that mineralogists describe as a framework.
Diamond forms at extremely high temperatures and pressures, conditions that are only possible very deep in the Earth’s crust or even the upper mantle. Large diamonds, particularly large diamonds without flaws, are extremely rare. These flawless diamonds are very valuable as gemstones. The vast majority of diamonds are small, flawed and colored by dark impurities. These impure diamonds are used in industrial uses.
Industrial diamonds make up more than half of the world’s production by weight. The weight of both gem and industrial diamonds is expressed in carats. One carat equals one fifth of a gram.
Diamond crystallizes in the isometric (cubic) system, and regularly forms cubes and octahedra (an octahedra is an 8-sided "diamond-shaped" crystal; see below).
In the diamond industry, the term "bort" is used for diamonds that have a rough, rounded form and which lack a distinct cleavage. Cleavage is the term used by mineralogists to describe the way some minerals break into flat surfaces. Bort refers to low grade, poor quality, industrial diamonds.
The name diamond is a corruption of the Greek word adamas which means invincible. It was given in reference to diamond’s great hardness.
Natural diamond has been discovered in approximately 35 different countries. Some diamonds have been found in the United States. Colorado, for instance, has produced a small number of diamonds.
Geologically speaking, natural diamonds are found in two environments. Most are found in kimberlites, which are pipe-like formations created as a result of volcanic and tectonic activity. Kimberlite is a blue rock typical of these pipes. The second source is placer deposits. The diamonds are easily weathered out of their kimberlite host rock and are washed away by streams and rivers. When these streams slow down, the diamonds are deposited in the stream sands in what are called placer deposits.
It is interesting to note that "synthetic diamond" is the form of diamond predominantly used in industry. The process allows the removal of impurities and produces a product with consistent physical properties; most of the carbon comes from graphite. Synthetic diamond accounts for the majority of industrial diamond consumption.
Because it is the hardest substance known, diamond will cut through any material. Consequently, it is used as an abrasive and in cutting and grinding applications. Industrial diamonds are embedded in large steel drill bits to drill into rock for wells to find water, oil, and natural gas. It is also important in the manufacture of machinery for drilling and cutting metal machine parts.
The United States is by far the world’s largest consumer and market for industrial diamonds. It is predicted that the U.S. will lead the world in diamond consumption well into the 21st century.
Substitutes and Alternative Sources
The mineral corundum can be used for some grinding and cutting applications since it is also an extremely hard mineral (number 9 on Mohs' hardness scale). Some manufactured materials can also be used in place of diamond, including carbon boron nitride, fused aluminum oxide, and silicon carbide.