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Lonsdaleite (named in honour of Kathleen Lonsdale), also called hexagonal diamond in reference to the crystal structure, is an allotrope of carbon with a hexagonal lattice, as opposed to the cubical lattice of conventional diamond.
Lonsdaleite is an allotrope sometimes called "hexagonal diamond", formed from graphite present in meteorites upon their impact on the earth. The great heat and pressure of the impact transforms the graphite into a denser form similar to diamond but retaining graphite's hexagonal crystal lattice. "Hexagonal diamond" has also been synthesized in ...
Rapid conversion of graphite to diamond requires pressures well above the equilibrium line: at 2000 K, a pressure of 35 GPa is needed. [10] Above the graphite–diamond–liquid carbon triple point, the melting point of diamond increases slowly with increasing pressure; but at pressures of hundreds of GPa, it decreases. [12]
In the first three months of 2024, 13.5% of diamond jewelry items sold in the U.S. were made with lab-grown stones, according to Edahn Golan, a diamond industry analyst.
When diamonds are grown by the high-pressure high-temperature technique, nickel, cobalt, chromium or some other metals are usually added into the growth medium to facilitate catalytically the conversion of graphite into diamond. As a result, metallic inclusions are formed.
The first lab-made diamonds can be dated back to the 1950s, [1] and memorial diamonds started to appear in the market in the early 2000s. More than one company has claimed to be the first to provide memorial diamonds, and both Heart In Diamond [2] and LifeGem [3] have claimed to have a patent covering the growing of a "personalized gem diamond".
At surface air pressure (one atmosphere), diamonds are not as stable as graphite, and so the decay of diamond is thermodynamically favorable (δH = −2 kJ/mol). [22] However, owing to a very large kinetic energy barrier, diamonds are metastable; they will not decay into graphite under normal conditions. [22]
The shock pressures from the impact instantaneously transformed graphite in the ground into diamonds within a 13.6 km (8.5 mi) radius of the impact point. These diamonds are usually 0.5 to 2 mm (0.020 to 0.079 in) in diameter, though a few exceptional specimens are 10 mm (0.39 in) in size.