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What is a diamond?
A diamond is a mineral composed of pure carbon. Known as the hardest naturally occurring substance, it is a popular gemstone valued for its hardness, brilliance, and sparkle.
Diamonds are formed in the Earth’s mantle at depths exceeding 75 miles (120 km). Over billions of years, carbon atoms bond in a crystal structure. Volcanic eruptions bring them to the surface, where they can be mined from kimberlite pipes, alluvial gravels, or glacial tills.
Diamonds vary in color from colorless to black and can be transparent, translucent, or opaque. The high refractive power and dispersion give diamonds their brilliance and fire. They are used industrially as cutting tools or abrasives.
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How are diamonds formed in nature?
In nature, diamonds form deep within the Earth's mantle, exceeding depths of 75 miles (120 kilometers), where extreme temperatures and pressures exist. Over billions of years, carbon atoms bond, creating a crystal structure that results in the hardest known natural substance. These diamonds are brought to the Earth's surface through volcanic eruptions. They can then be mined from kimberlite pipes, alluvial gravels, or glacial tills.
Since 1955, diamonds have also been made synthetically. This process involves high pressure and temperature, using a solvent or catalyst like iron.
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Why are diamonds considered gemstones?
Diamonds are considered gemstones because they possess beauty, durability, and rarity, which are the prime requirements for a gem. Their hardness, brilliance, and sparkle make them unsurpassed as gems. In the symbolism of gemstones, the diamond represents steadfast love and is the birthstone for April. Gemstones have been admired by humankind since ancient times and have long been used for jewelry. Diamonds are highly prized and, like other gemstones, are cut and polished for use in jewelry.
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What are the main uses of diamonds as gemstones?
Diamonds are prized as gemstones for their exceptional hardness, brilliance, and sparkle. These qualities make them unsurpassed in jewelry. The most popular cut for diamonds is the brilliant cut, which has 58 facets, though other cuts, called fancy cuts, include the marquise, emerald, and pear shape.
Because of their connection to steadfast love, diamonds are often used in engagement and wedding rings. The slogan, "a diamond is forever" has further cemented the popularity and durability of diamonds in the cultural consciousness.
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What are the '4 Cs' used to grade diamond gemstones?
Diamonds are graded by the "4 Cs": cut, clarity, carat, and color.
- Cut The angles of the facets must be exact to yield maximum brilliancy, and their sizes must be accurately regulated to preserve symmetry.
- Clarity Most diamonds used as gems are transparent and colorless or nearly so.
- Carat Diamond stones are weighed in carats (1 carat = 200 milligrams) and in points (1 point = 0.01 carat). The weight of a carat is based on the weight of the carob seed, which was once used as a weighing standard by jewelers in Africa and the Middle East.
- Color Colorless or pale blue stones are most valued, but these are rare; most gem diamonds are tinged with yellow. A “fancy” diamond has a distinct body color; red, blue, and green are rarest, and orange, violet, yellow, and yellowish green more common.
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How are synthetic (lab-made) diamonds different from natural diamonds?
Natural diamonds form over billions of years deep within the Earth's mantle under immense pressure and heat, resulting in a crystal structure of carbon atoms. They are brought to the surface through volcanic eruptions and mined from kimberlite pipes, alluvial gravels, or glacial tills.
Synthetic diamonds are man-made, typically produced by subjecting graphite to high temperatures and pressures. Two common methods include high-pressure high-temperature (HPHT) and chemical vapor deposition (CVD). In the HPHT method, a diamond seed is surrounded with carbon and subjected to high pressures and temperatures until the carbon melts and crystallizes around the seed. In the CVD method, a diamond seed is placed in a chamber containing a gas like methane. When the chamber is heated, the carbon in the methane crystallizes on the seed.
While synthetic diamonds share fundamental properties with natural diamonds, large, gem-quality synthetic diamonds are rare due to the high cost of synthesis. Most are produced as grit or small crystals for industrial applications.
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diamond, a mineral composed of pure carbon. It is the hardest naturally occurring substance known; it is also the most popular gemstone. Because of their extreme hardness, diamonds have a number of important industrial applications.
The hardness, brilliance, and sparkle of diamonds make them unsurpassed as gems. In the symbolism of gemstones, the diamond represents steadfast love and is the birthstone for April. Diamond stones are weighed in carats (1 carat = 200 milligrams) and in points (1 point = 0.01 carat). In addition to gem-quality stones, several varieties of industrial diamonds occur, and synthetic diamonds have been produced on a commercial scale since 1960. (See also industrial diamond; synthetic diamond.)
Diamonds are found in three types of deposits: alluvial gravels, glacial tills, and kimberlite pipes. The kimberlite pipes (such as those at Kimberley, South Africa) form from intrusions of magma into the Earth’s crust and deliver diamonds and other rocks and minerals from the mantle. The pipes themselves are often less than 100 million years old. However, the diamonds they carry were formed 1 to 3.3 billion years ago at depths of more than about 75 miles (120 km). Diamonds found in alluvial and glacial gravels must have been released by fluvial or glacial erosion of the kimberlite matrix and then redeposited in rivers or in glacial till.
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Diamonds vary from colorless to black, and they may be transparent, translucent, or opaque. Most diamonds used as gems are transparent and colorless or nearly so. Colorless or pale blue stones are most valued, but these are rare; most gem diamonds are tinged with yellow. A “fancy” diamond has a distinct body color; red, blue, and green are rarest, and orange, violet, yellow, and yellowish green more common. Most industrial diamonds are gray or brown and are translucent or opaque, but better-quality industrial stones grade imperceptibly into poor quality gems. The color of diamonds may be changed by exposure to intense radiation (as released in a nuclear reactor or by a particle accelerator) or by heat treatment.
A very high refractive power gives the diamond its extraordinary brilliance. A properly cut diamond will return a greater amount of light to the eye of the observer than will a gem of lesser refractive power and will thus appear more brilliant. The high dispersion gives diamonds their fire, which is caused by the separation of white light into the colors of the spectrum as it passes through the stone.
The scratch hardness of diamond is assigned the value of 10 on the Mohs scale of hardness; corundum, the mineral next to diamond in hardness, is rated as 9. Actually, diamond is very much harder than corundum; if the Mohs scale were linear, diamond’s value would be about 42. The hardness of a diamond varies significantly in different directions, causing cutting and polishing of some faces to be easier than others.
In the atomic structure of diamond, as determined by X-ray diffraction techniques, each carbon atom is linked to four equidistant neighbors throughout the crystal. This close-knit, dense, strongly bonded crystal structure yields diamond properties that differ greatly from those of graphite, native carbon’s other form.
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