Diamond is a single-element crystal composed of carbon. It is the hardest known mineral in nature. Its core characteristics can be summarized in terms of structure and physicochemical properties:
1. Crystal Structure Characteristics
The carbon atoms in diamond form a tetrahedral three-dimensional network structure through sp³ hybridization. Each carbon atom forms covalent bonds with four surrounding carbon atoms, belonging to the isometric crystal system (cubic crystal system). Natural crystals often exhibit octahedral, dodecahedral, or hexoctahedral morphologies, and the crystal faces often show rounded melting characteristics.
2. Core Physical Properties
Hardness: With a Mohs hardness of 10, it is the hardest naturally occurring substance. Its microhardness can reach 7000-10000 kg/mm², with the octahedral crystal face exhibiting the highest hardness.
Optical Properties: It has a high refractive index of 2.417 and a dispersion rate of 0.044, possessing a unique adamantine luster. Its crystal faces can decompose white light, creating dispersion (fire effect). Pure diamond is colorless and transparent; trace elements can impart different colors such as yellow, brown, blue, and red.
Other Physical Properties: It has a density of approximately 3.52 g/cm³, excellent thermal conductivity (approximately 2000 W/m·K at room temperature, up to four times that of copper), is non-conductive, and possesses oleophilic, hydrophobic, and triboelectric properties.
Luminescence: It exhibits a pale blue phosphorescence when exposed to sunlight and typically fluoresces sky blue under X-ray irradiation.
3. Chemical Properties
It is chemically very stable and does not react with acids or alkalis at room temperature. It is an inert carbon element, containing only small amounts of impurity elements such as Si, Mg, Al, N, and B. The types of impurities affect the type and color of diamond.
