Mineral composed of pure carbon, the hardest naturally occurring substance known and a valuable gemstone. Diamonds are formed deep in the Earth by tremendous pressures and temperatures over long periods of time. In the crystal structure of diamond, each carbon atom is linked to four other, equidistant, carbon atoms. This tight crystal structure results in properties that are very different from those of graphite, the other common form of pure carbon. Diamonds vary from colourless to black and may be transparent, translucent, or opaque. Most gem diamonds are transparent and colourless or nearly so. Colourless or pale blue stones are most valued, but most gem diamonds are tinged with yellow. Because of their extreme hardness, diamonds have important industrial applications. Most industrial diamonds are gray or brown and are translucent or opaque. In the symbolism of gemstones, the diamond represents steadfast love and is the birthstone for April.

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