The most convincing evidence that coal did not play a role in the formation of most diamonds is a comparison between the age of Earth’s diamonds and the age of the earliest land plants. Most of the rock-hosted diamond deposits that have been found were formed during the Precambrian Eon – the span of time between Earth’s…

In the 1950s, new methods of diamond formation were discovered on Earth’s surface. Scientists were able to create the temperature and pressure conditions needed to create diamonds in a lab. Most of the early diamonds were not gem quality, but they were perfect for use as abrasive granules in drill bits, cutting tools, and grinding…

NASA researchers have detected large numbers of nanodiamonds in some meteorites. (Nanodiamonds are diamonds that are a few nanometers – billionths of a meter in diameter.) About three percent of the carbon in these meteorites is contained in the form of nanodiamonds. These diamonds are too small for use as gems or industrial abrasives; however, they are a…

Throughout its history, Earth has been repeatedly hit by large asteroids. When these asteroids strike the earth, extreme temperatures and pressures are produced. For example: when a six mile (10 kilometer) wide asteroid strikes the earth, it can be traveling at up to 9 to 12 miles per second (15 to 20 kilometers per second). Upon…

Tiny diamonds have been found in rocks that are thought to have been subducted deep into the mantle by plate tectonic processes – then returned to the surface. (See Location 2 in the diagram at the top of the page.) Diamond formation in a subducting plate might occur as little as 50 miles (80 kilometers)…

Geologists believe that the diamonds in all of Earth’s commercial diamond deposits were formed in the mantle and delivered to the surface by deep-source volcanic eruptions. These eruptions produce the kimberlite and lamproite pipes that are sought after by diamond prospectors. Most of these pipes do not contain diamond, or contain such a small amount of diamond…

Many people believe that diamonds are formed from the metamorphism of coal. That idea continues to be the “how diamonds form” story in many science classrooms. Coal has rarely – if ever – played a role in the formation of diamonds. In fact, most diamonds that have been dated are much older than Earth’s first land plants…

Diamond formation: Diamonds found at or near Earth’s surface have formed through four different processes. The plate tectonics cartoon above presents these four methods of diamond formation. Additional information about each of them can be found in the paragraphs and small cartoons below.