diamond

Diamond is the crystalline form of carbon. It is renowned for exceptional hardness, a high melting point, and striking optical properties. The name comes from the Greek adamas, meaning invincible. Natural diamonds occur in a range of colors from colorless to yellow, brown, blue, pink, and green, often influenced by trace impurities or lattice defects. Synthetic diamonds are produced commercially and share the same crystal structure and many physical properties.

Diamond has a face-centered cubic crystal lattice. Each carbon atom bonds covalently to four neighbors in a tetrahedral arrangement, creating exceptionally strong bonds. This structure gives diamond its hardness (10 on the Mohs scale) and its very high thermal conductivity, typically well above 1000 W/m·K. Diamond is highly transparent and has a high refractive index (about 2.417) and strong dispersion, which contribute to its brilliance. It is chemically resistant but can cleave along {111} planes, making it subject to fracture if struck along a cleavage plane.

Most natural diamonds form deep in Earth's mantle under high-pressure, high-temperature conditions and are brought to the surface by deep-source volcanic eruptions through kimberlite pipes. They can also be found in alluvial deposits where river transport concentrates eroded diamonds. Diamond production is complemented by extensive synthetic production using high-pressure high-temperature (HPHT) or chemical vapor deposition (CVD) methods.

Uses include jewelry, where color, clarity, cut, and carat determine value, and industrial applications in cutting, grinding, and drilling, where abrasive properties are essential. Synthetic diamonds are widely used in tooling and optics, and continue to influence markets for natural gems.