Diamond

Properties and Thermodynamics

• Diamond is a solid form of pure carbon with a diamond cubic crystal structure.
• It has the highest hardness, thermal conductivity, and refractive index of any natural material.
• Most natural diamonds have ages between 1 billion and 3.5 billion years.
• Synthetic diamonds can be grown from high-purity carbon under high pressures and temperatures.
• The equilibrium pressure and temperature conditions for the transition between graphite and diamond are well established.
• Diamond is metastable at normal temperature and pressure, with graphite being the stable phase of carbon.
• Rapid conversion of graphite to diamond requires pressures above the equilibrium line.
• The melting point of diamond increases with increasing pressure, but at very high pressures, it decreases.
• Diamond can melt into a metallic fluid at ultrahigh pressures and temperatures.

Crystal Structure

• The most common crystal structure of diamond is diamond cubic.
• The unit cell of diamond has a length of 3.567 angstroms.
• Diamond cubic lattice can be thought of as two interpenetrating face-centered cubic lattices.
• Diamonds can also form a hexagonal diamond or lonsdaleite structure.
• Diamond can have various crystal habits, including euhedral or rounded octahedra and twinned octahedra.

Main Diamond Producing Countries

• Diamond is a solid form of carbon with high hardness and thermal conductivity.
• Diamond anvil cells can subject materials to high pressures found deep in the Earth.
• Different colors in diamonds are caused by small numbers of defects or impurities.
• Natural, synthetic, and imitation diamonds can be distinguished using optical techniques or thermal conductivity measurements.

Uses and Applications

• Diamond is used in major industrial applications such as cutting and polishing tools.
• It has high thermal conductivity, sound velocity, and low adhesion and friction.
• Diamond's optical transparency extends from the far infrared to the deep ultraviolet, with high optical dispersion.
• Diamond is chemically inert, not reacting with most corrosive substances, and has excellent biological compatibility.

Geology and Exploration

• Diamonds are extremely rare, with concentrations of at most parts per billion in source rock.
• They are found in kimberlites on the oldest part of cratons, as well as in lamproites and lamprophyre rocks.
• Geophysical methods like aeromagnetic surveys and electrical resistivity aid in identifying promising regions for diamond exploration.
• Diamonds are dated using radioactive isotopes, with kimberlite diamonds having ages between 1 and 3.5 billion years.
• Gem-quality diamonds come from depths of 150-250km in the lithosphere, specifically from mantle keels.

Diamond Data Sources