Diamonds have captivated humanity for centuries, admired for their sparkle and strength. These gemstones are more than just beautiful adornments; they are also materials with unique properties used in various industries. Understanding what constitutes a diamond and how it acquires its characteristics reveals its fundamental nature.
The Elemental Building Block
A diamond is composed almost entirely of a single element: carbon. Diamonds are typically 99.95 percent carbon, with the remaining small percentage consisting of trace elements that can influence their color or crystal shape. Carbon atoms possess four valence electrons, allowing them to form strong chemical bonds. In a diamond, each carbon atom forms four bonds with neighboring carbon atoms, creating a dense, three-dimensional network.
Other carbon forms, like graphite, also consist solely of carbon but exhibit vastly different properties due to their atomic arrangement. Graphite’s carbon atoms bond with only three others, forming flat, hexagonal layers held by weak forces, which makes it soft and slippery, unlike diamond.
How Diamonds are Formed
Diamonds originate deep within the Earth’s mantle, under conditions of extreme heat and pressure that are rarely found elsewhere. This formation occurs at depths of 140 to 190 kilometers (87 to 118 miles) below the surface. Temperatures average 900 to 1,300 degrees Celsius (1,650 to 2,370 degrees Fahrenheit), with pressures reaching 4.5 to 6 gigapascals, about 45,000 to 60,000 times atmospheric pressure. These intense conditions force carbon atoms to crystallize into diamond’s dense, stable structure.
Once formed, diamonds are transported from these depths to the Earth’s surface through a unique geological process. This occurs via rapid volcanic eruptions that bring molten rock, known as kimberlite or lamproite magma, from the mantle. These magmas ascend quickly, forming carrot-shaped vertical structures called kimberlite pipes. The speed of these eruptions is crucial, as it allows diamonds to be carried to the surface before reverting to graphite, which is the more stable form of carbon at lower pressures. Diamonds found in these pipes are xenocrysts, meaning they formed prior to and were carried by the erupting magma.
Structure and Unique Properties
The properties of diamond stem directly from its unique atomic structure. Each carbon atom within a diamond is covalently bonded to four other carbon atoms, forming a robust, repeating three-dimensional pattern known as a diamond cubic structure. This rigid, interlocking network of strong covalent bonds accounts for diamond’s status as the hardest known natural material, scoring a 10 on the Mohs hardness scale.
Beyond its hardness, this tightly bonded structure also gives diamond other characteristics. It exhibits brilliance and “fire” due to its high refractive index and moderate dispersion, which cause light to bend and split into spectral colors. Diamond also has the highest thermal conductivity of any natural material, meaning it conducts heat very efficiently. This property is so pronounced that thermal probes are used to distinguish real diamonds from imitations. Because all its valence electrons are involved in strong covalent bonds, diamonds are excellent electrical insulators.