When carbon atoms are tetrahedrally bonded together, they create a transparent crystal of pure carbon that we call a diamond. Diamonds have remarkable physical characteristics, including their extremely hard structure, a high dispersion rate, and high thermal conductivity. These properties are a result of atoms in the diamond crystal being arranged in a tetrahedral, and have allowed people to adapt diamonds for many uses. Graphite is an allotrope of carbon, yet due to its rhombohedral crystal structure, it is soft, dark gray and opaque, unlike diamond crystals. A polymorph of diamonds, lonsdaleite, has a hexagonal structure, which is rarely found in nature, but is one of the characteristics found in synthetic diamonds. A spherulite is a gray or black, colorless diamond that has a small radial structure.
The main difference between diamond and graphite is the crystal bond structure that gives diamonds their hardness. Diamonds score a 10 on the Mohs scale that rates a mineral's hardness; this makes diamonds the hardest material that occurs naturally. In fact, diamonds get their name from their extremely hard nature. In 2005, an allotrope of carbon was synthesized to form aggregated diamond nanorods, which are even harder than diamonds. New South Wales, Australia produces the hardest diamonds in the world, which tend to be small and perfect to imperfect octahedra, and are often used to polish other diamonds. While most diamonds show signs of multiple growth stages, diamonds found in New South Wales tend to only have a single stage growth crystal, which makes them harder than others. Multiple growth stages tend to create flaws that affect hardness. Out of the over 3,000 known minerals, diamonds are considered the most useful. The hardness of a diamond makes them perfect for cutting, polishing and wearing away any material, even other diamonds. Diamond powder can be used as an abrasive, and often saws and drill bits will have diamond tips. Diamonds are also used as semiconductors. Diamonds are an ideal gemstone, only able to be scratched by other diamonds. They maintain their polish well, keeping their luster for years. Diamonds are the preferred gemstone for engagement and wedding rings, because they are resistant to scratching, allowing them to be worn daily.
One of the characteristics that gemstones are judged by is their toughness. Toughness indicates the ability a material has to avoid breaking under impact, whereas hardness only refers to a materials ability to resist scratches. The toughness of diamonds is only rated fair to good. The macroscopic geometry of a material has an affect on its toughness, and therefore, different diamond cuts are more prone to breaking.
Diamonds can be found in a variety of hues, from colorless to colored black. Defects and impurities cause coloration in diamonds. If these impurities produce a detectable hue, the diamond is considered to be a colored diamond, whereas pure diamonds are translucent or colorless. A yellow or brown tinge is fairly common as an imperfection, and is caused by nitrogen.
One of the major attractive qualities of diamonds is their ability to split white light, and show all of its component colors. The high dispersion property of diamonds produces what is referred to as "fire." Luster is the term used to describe how light interacts with a crystal's surface, and diamonds have a brilliant luster.
