Characteristics of Natural Diamonds

Compressed deep within the earth, diamonds are hard but not necessarily tough.

Diamonds may be made by humans or by natural processes. The latter type come at a high cost. Natural diamonds are associated with the controversy of bloody civil wars and environmentally unsound mining practices, as well as with the throes of enduring love. Many natural diamonds do not become gemstones at all, but serve industrial purposes. Within the world of natural diamonds, flaws and variation abound. However, essential identifying characteristics remain.

Hardness and Toughness

A mineral's hardness refers to its resistance to being scratched. On the Mohs scale of hardness, the natural diamond is a 10, the highest value. Toughness measures a material's resistance to fracture when impacted under stress, in pounds-force per square inch. The natural diamond is fair to good in toughness, and may be prone to breakage, depending on the cut.

Density

A natural diamond's density of 3.51 grams per cubic centimeter is remarkable -- the mineral has a high mass in relation to its volume. This is a result of the natural diamond's carbon atoms being compressed together tightly under high-pressure conditions.

Fluorescence

Some natural diamonds exhibit fluorescence, the ability to absorb a high-energy photon and re-emit it as a lower-energy photon to "glow" as visible light. This phenomenon can manifest as different colors when under ultraviolet light, and as greenish yellow under X-rays. Diamonds that retain this light after the light source has been turned off are called phosphorescent.

Composition

Natural diamonds are composed of carbon crystals that have been created inside the earth under great pressure and high temperatures. When a diamond contains certain impurities, such as nitrogen, it may display coloration changes. For example, Type 1 diamonds contain nitrogen impurities. Type 1-B diamonds are yellowish from widely distributed impurities, whereas Type 1-A diamonds have nitrogen in clustered form, and are not affected in color. A natural diamond can contain both types of impurities.

Electrical Conduction

Natural diamonds make poor electrical conductors due to their transparency but make good electrical insulators, or nonconductors. However, some natural blue diamonds can act as semiconductors, or moderate electricity conductors.

Thermal Conductivity

Providing high thermal conductance, or the ability to extract heat, natural diamonds are used by semiconductor manufacturers to keep other materials from overheating. The conductivity is possible due to a natural diamond's structural strength, which helps vibrational energy travel via the mineral's strong internal network of chemical bonds.

References

• Lieber and Solow; Natural Diamonds -- From Mines to Machines; Steve Roffman; July 2000
• European Jeweler and Goldsmith: Diamond Chemistry and Composition
• American Museum of Natural History: The Nature of Diamonds