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Diamonds can be natural or synthetic; Mechanical Properties Optical Properties Natural diamonds; • • • • Lustrous (shiny) • Pure diamond is the most transparent material known • High dispersion and high refractive index • Natural diamond is formed when carbon crystallizes • Pressure must be between 45 and 60 kilo bars and the temperature between 900 and 1300 °C. • These conditions occur naturally only in the lithospheric mantle, below the continental plates, and at meteorite crash sites • Natural diamond sources have been discovered in approximately 35 different countries • The most notable diamond deposits are in Africa • Hard-hardest natural material on earth. (10 Mohs) The least compressible and stiffest substance Brittle-splits along its crystal cleavage planes when receiving a certain impact Dense-despite low atomic weight of carbon Synthetic; • Produced by the process of HPHT (High Pressure Temperature Synthesis) • Graphite and a metallic catalyst are placed in a hydraulic press under high temp. and pressures for a couple of hours • Graphite is converted to diamonds • usually to small and too flawed to use as gemstones • But useful on drill bits and cutting tools Did you know? Chemical Properties Structure and bonding • • • • Giant molecular structure. Each carbon atom is covalently bonded to four other carbon atoms Covalent bonds are strong Contains many covalent bonds therefore a lot of energy is required to separate the atoms in a diamond (high ionization energy) • High melting point and boiling point • Is an allotrope of carbon • • • • • • • Insoluble in water High melting and boiling point Negative electron affinity Good chemical stability does not react with acid and alkali under room temperature, so acid and alkali can be used to refine synthetic diamonds Allotropes of carbon include diamond, graphite and soot. all are forms of the element carbon - each have chemical symbol C Allotropes of carbon differ greatly in their structure and properties • Diamonds are the hardest, natural substance on earth • Diamonds are brought closer to the earth’s surface through volcanic activity • The earliest written proof of the existence of diamonds dates back to around 500BC • The rarest colours of diamonds are red and blue • The Kimberley mines have produced some of the most famous diamonds, some that even the Queen of England wears. School: Deutsche Internationale Schule Johannesburg Teacher: Mrs Machlachlan Learners: Neil Hiestermann, Rebecca Organ, Sebastian Welke