Diamond precious gemstone index and mineral information

The most precious of the four precious stones, including emeralds, rubies and sapphires; diamonds are the hardest substance in the universe. Its name derives from the Greek word adamas, meaning invincible. The diamond is the only precious stone that rates a number ten in Moh’s scale of hardness. Made of pure carbon the only thing that can cut a diamond is a diamond.  Its extreme hardness is the result of its atoms being compacted and bonded by high pressures and high temperatures in the Earth’s upper mantle. Because diamond is made up of carbon, it burns in oxygen or in air heated to a very high temperature.

Most diamonds came from alluvial deposits, (mainly river and beach gravels) until the discovery in the mid-19th century in South Africa, of pipe-like intrusions that had risen from great depths, and were filled with a variety of peridotite. Peridotite was later named kimberlite, because of it being first identified in Kimberley, South Africa. This igneous rock is rich in magnesium, iron, and calcium. These intrusions are also found in lamproitic rocks, which are the source of diamonds in Western Australia. Intrusions can remain deep in the Earth until volcanic eruptions force them to the surface.

In the past, diamonds were extracted by panning from weathered kimberlite in open pits, but as the pits became deeper and the rock harder, underground mining became necessary. Today, drill-holes are packed with explosives and blasted to break up the rock. It is brought to the surface and the diamonds are separated using grease tables.

Diamonds occur in two distinct varieties. Bort, which occurs as rough rounded masses with radial or confused structure, without distinct cleavage; it is grayish black with a specific gravity of 3.5. Carbonado, or black diamond, is opaque, granular to compact, and without cleavage; its specific gravity 3.1 to 3.3.

Crystals may be transparent, translucent, or opaque, and range from colorless to black, with brown and yellow being the most common colors. Colorless or pale blue gemstones are the most often used in jewelry. Red and green have long been considered the rarest colors, but pure orange and violet are much rarer and also more valuable.

Diamonds are measured in carats. The value of a carat has been standardized as 0.2 grams or 200 milligrams since 1907. The term “carat” is believed to derive from the weight of Mediterranean carob seed pods from the “locust pod” tree (Ceratonia siliqua), which have long been used to weigh precious stones. The name is derived from the Greek term keration, meaning “fruit of the carob.”

Diamonds have a perfect crystal form and high symmetry. Uncut crystals may look greasy and rounded, but when broken or cut, the faces show brilliant adamantine (diamond-like) luster and dispersion. These give the stone a fiery brilliance that is probably best displayed by brilliant cuts, which are the most popular today. Diamonds are generally insensitive to chemical reactions. High temperatures can produce etchings on the facets. Due to the optical effects, the high hardness, and its rarity, the diamond is considered the king of gemstones. It has been used for adornment since ancient times.

In ancient times, diamonds were thought to bring victory to the wearer, giving him superior strength, fortitude and courage. They were associated with thunder and lightning. It was also believed to indicate guilt or innocence, the stone growing dim if the accused was guilty and shining brightly if he was innocent. They were also believed to possess reproductive powers.

Since the late 19th century, South Africa has been the major source of gem-quality diamonds. Australia is a major producer of fancy colors. The Democratic Republic of Congo (formerly Zaire) once produced the largest quantity of diamonds, almost all being of industrial grade. Today more than twenty countries belong to the diamond suppliers circle. Important diamond producers include Botswana, Guinea, Russia, China, The United States, Brazil, Venezuela, Canada, and the Argyle and Merlin diamond mines in Australia.

The sale and distribution of diamonds is strictly controlled by the Diamond Trading Corporation to maintain a stable market. Diamond is known as the month of April’s birthstone meaning, innocence.

Mohs’ Hardness: 10