A Little Science
PostBy Avi Paz Group At 01.09.2010
The word "diamond" is derived from the Greek adamas ("unbreakable"). A diamond – one of two forms of pure carbon, the other being graphite – is formed from carbon atoms are bonded tetrahedrally, forming a transparent crystal noted for both its hardness and thermal conductivity – the highest of any bulk material.
The carbon atoms in a diamond form a rigid structure known as the diamond lattice. The lattice allows only a very few types of impurities through, which is what gives most diamonds their clear, colorless appearance. Paradoxically, small amounts of "impurities" in the form of exposure to the elements boron or nitrogen can result in fancy colored diamonds.
Most natural diamonds originate over the course of one to three billion years and are formed in the Earth's mantle at depth of 140 to 190 km (87 to 120 miles) from the carbon contained in other minerals.
Volcanic eruptions propel magma through cracks in the Earth's surface. The magma cools into rock types known as kiberlites and lamproites, which contain the diamonds.
Anyone interested in reversing the process should be advised that in a vacuum or oxygen-free atmosphere at temperatures above 1,700 °C (1,973 K / 3,583 °F), diamond converts to graphite. When air is present, the diamond-to-graphite transformation starts at ~700 °C. The density of natural diamonds ranges from 3.15–3.53 g/cm3, with pure diamond close to 3.52 g/cm3.
Diamond is the hardest material found in nature and is rated a 10 on the Mohs scale of mineral hardness. But the degree of hardness in a particular diamond might vary depending on the stone's purity, orientation, and crystalline perfection. Diamonds' hardness means that they retain polish and resist scratching, making them coveted gemstones.
While diamonds are hard, they are also brittle. Diamonds feature a cleavage plane, which contributes to their breakability depending on their orientation. Natural diamonds have a toughness rating of 2.0 MPa•m1/2 and a critical stress intensity factor of 3.4 MN•m−3/2.
