handbook of carbon, graphite, diamond and fullerenes

12
Natural and High-Pressure Synthetic
Diamond
1.0 INTRODUCTION
Rough diamonds, that is, uncut and unpolished, were known and
prized in antiquity. They were first reported in India 2700 years ago. From
India, diamond trading moved gradually westward through Persia and the
Roman Empire. However the full beauty of diamond was not uncovered
until faceting and polishing techniques were developed in the 14th and 15th
centuries. A detailed history of diamond is given in Refs. 1 and 2.
Unlike graphite and carbon materials, diamond is very rare and, with
opal and ruby, considered the most valuable mineral, known the world over
as a gemstone of perfect clarity, brilliance, hardness, and permanence.
Diamond is produced in nature at high pressure and temperature in
volcanic shafts. The high-pressure synthesis essentially duplicates this
natural process and both materials, the natural and the synthetic, have
similar properties and are reviewed together in this chapter.
2.0 NATURAL DIAMOND
2.1 Occurrence and Formation of Natural Diamond
The two major allotropes of the element carbon, graphite and diamond,
occur in igneous rocksJ 3 ' As seen in Ch. 11, at ordinary pressures
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