Diamond is a crystallized form of carbon which forms under special combinations of pressure and temperature that are not present at the earth's surface except in man-made contraptions which reproduce a diamond's pressure-temperature formation regime (ie synthetic diamonds created from methane gas through a process called chemical vapor deposition). It is possible to produce a near infinite amount of synthetic diamonds, but the supply of natural diamonds is limited to what magmas entrain in the mantle where diamonds grow and transport to the earth's surface in the form of kimberlite pipes that erupt or emplace as dykes and sills that chill before breaking the earth's surface. Unlike the element gold which has the same market value regardless of its physical form, a rough diamond's value depends on its crystal form which manifests itself in the so-called 4 C's: color (with "white" meaning no color at all), clarity (no impurities within the crystal that cloud it or disrupt the sparkle), cut (the crystal shape which is not always an octahedron, and whose value hinges on how much waste cutting will produce), and carats (the weight of the diamond - its size). These 4 factors combine to create thousands of price categories. In simple terms, a colorless, flawless octahedron will be more valuable on a per carat basis the larger the size. Although synthetic and natural diamonds are chemically identical, the synthetic diamond is a disposable consumer item whereas a natural diamond is a collectible. The value of a gem diamond is thus defined not by its function but by its perception. That perception came under siege when consumers learned that diamonds from certain regions embroiled in civil conflict were being produced under horrific human conditions and sold to fund the ongoing conflicts, primarily in Africa. These "blood" diamonds represented a very small portion of global diamond supply but threatened to taint all diamonds as a cosmetic-fashion product to avoid. That would have been unfortunate because responsibly operated diamond mines underpin a voluntary wealth transfer from the buyers of diamonds to everybody involved in the supply chain. Nobody needs a gem diamond for anything so its high value is exchangeable only among the world's economic elites. The existence of diamonds does not matter to people concerned about healthcare, food, shelter and other basics of life. The role of natural diamonds as a voluntary wealth transfer mechanism creates a public good which would have disappeared if there was no response to the conflict diamond problem. That response was the Kimberley Process to create a source certification system that reassured consumers that the diamonds they purchased were "clean". And it turns out that KP is quite helpful in enabling consumers to distinguish natural collectibles from factory disposables. Once the KP was established the task of compiling diamond supply and value statistics shifted from Bram Janse to the Kimberley Process which has published Annual Statistics since 2004. The data for 1980-2003 is courtesy of Bram Janse while the rest is from the KP. In addition to facilitating wealth transfer another good indirectly created by diamonds is in the realm of knowledge creation about the earth's geological history. While a consumer desires a diamond with no inclusions, those lower value "dirty" diamonds are like suitcases that transported data from the mantle without it being transformed during the magma's ascent. Patricia Sheahan has devoted much of her career documenting both the scientific and media literature related to diamonds which is presented in the KRO Diamond Resource Center as the Sheahan Diamond Literature Reference Compilation (see SDLRC Q&A for background). Every month the SLDRC references compiled by Patricia Sheahan are incorporated into an online database going back to 1850.
Diamonds, like other gemstones, and unlike most metals, are not uniformly priced on the basis of weight but rather on the weight and quality of individual crystals. While the volume is uniformly measured by the carat weight, the annual supply statistics in terms of carat volume is not meaningful because each nation's production has a unique range of stone size and quality. To capture the importance of diamond production for a nation and the global supply it is necessary to present production in terms of annual value for the volume of carats produced. The value per carat is the total value divided by carat volume which conveys information about the quality and size of diamonds a nation produces. The first batch of graphics present production in volume terms, the second batch presents production value average carat value and percentage of global value statistics, and the third batch presents annual production value for individual countries and the percentage of annual global value ordered from highest to lowest for the most recent year data is available. The current data goes back to 1930 for the main producers, but does not include data before 2000 for West African countries because their production was presented as West Africa for the various data sources. Bram Janse, who has kept track of rough diamond production, write an article in 2007 for Gems & Geology that provides a good overview: Global Diamond Production since 1870.