Diamond is crystallized carbon, the hardest natural material known and one of the most studied gems in the world. This section covers how diamonds form, how they are graded and cut, how lab-grown stones compare with mined ones, and how rough moves from mine to jewelry counter.
What a diamond is
A diamond is pure carbon arranged in a tight cubic lattice in which every atom bonds strongly to four neighbors. That structure gives diamond a 10 on the Mohs hardness scale, high thermal conductivity, and a refractive index of about 2.42, which bends light sharply and gives a well cut stone its brilliance. Graphite is also pure carbon, but its atoms sit in weakly linked sheets, so it is soft. The diamond chemistry and formation page explains the difference, including the Type Ia, Ib, IIa and IIb classes based on nitrogen and boron.
Most natural diamonds formed roughly 150 to 200 kilometers below the surface, beneath old, stable parts of the continents called cratons, and many are one to over three billion years old. Volcanic eruptions carried them up in kimberlite and lamproite pipes. See diamond geology for the full story.
The 4Cs
Diamonds are graded on color, clarity, cut and carat weight, a system GIA developed and popularized in the mid-20th century. Color for white diamonds runs on a letter scale from D (colorless) to Z (light yellow or brown). Clarity runs from Flawless to Included and describes the size, number and visibility of inclusions and blemishes. Cut grades describe how well the proportions and finish return light. Carat is weight, with one carat equal to 0.2 grams.
The diamond 4Cs guide explains how the four factors interact, with separate pages on each one. Diamonds beyond the normal color range, such as strong yellow, pink or blue, are graded on a different scale described in fancy colored diamonds.
Natural and lab-grown diamonds
Lab-grown diamonds are real diamonds with the same carbon crystal structure and properties as mined ones. General Electric produced the first reproducible synthetic diamonds in the 1950s using high pressure and high temperature (HPHT). Chemical vapor deposition (CVD), which builds diamond from carbon-rich gas, became a major gem method in the 2010s. Lab-grown stones are now common in jewelry and generally sell for much less than natural diamonds of similar grade. Trained gemologists and lab instruments can tell the two apart, and U.S. FTC guidance says lab-grown stones must be clearly disclosed. Read more in lab-grown diamonds.
Lab-grown diamond is different from a simulant, which only imitates diamond. Cubic zirconia and moissanite are the most common simulants, and the how to tell if a diamond is real guide covers how testers separate them.
Cutting
Rough diamond is planned, sawn or cleaved, shaped and polished, and the cut decides how much light and fire a stone shows. The modern round brilliant, with 57 or 58 facets, is the most popular shape. Its proportions owe a lot to Marcel Tolkowsky's 1919 analysis. Older styles such as the rose cut and old European cut were designed for candlelight. Start with how diamonds are cut and the history of diamond cutting.
Mining and trade
For most of history, diamonds came from riverbeds in India, especially the region around Golconda. Brazil took over as the main source in the 18th century, and South Africa followed after the discoveries of 1867. In the 20th century De Beers controlled much of the world's rough supply. Major production later came from Botswana, Russia, Canada, Australia and other countries, and Australia's Argyle mine, famous for pink diamonds, closed in 2020.
The diamond mines of the world page surveys producing countries. The diamond pipeline traces how rough stones are sold, cut in centers such as Surat and Antwerp, and set into jewelry. The conflict diamonds page covers the civil wars of the 1990s and the Kimberley Process certification scheme that followed in 2003.
Buying a diamond
If you are shopping, read the 4Cs pages first, then diamond certificates and grading reports, which explains how to read a lab report and verify it. Diamond treatments covers fracture filling, laser drilling and color treatment.
Frequently asked questions
Are lab-grown diamonds real diamonds?
Yes. They have the same chemistry, crystal structure and physical properties as natural diamonds. They must be disclosed as lab-grown when sold.
How old are natural diamonds?
Most natural diamonds are between about one billion and over three billion years old, usually much older than the volcanic rocks that carried them to the surface.