What is Diamond?
Diamond is a rare, naturally-occurring mineral composed of carbon.
Each carbon atom in a diamond is surrounded by four other
carbon atoms and connected to them by strong covalent
bonds. This simple, uniform, tightly-bonded arrangement yields
one of the most durable substances known.
Diamond is a fascinating mineral. It is chemically resistant
and it is the hardest known natural substance. These properties
make it suitable for use as a cutting tool and for other
uses where durability is required. Diamond also has special
optical properties such as a high index of refraction, high
dispersion and high luster. These properties help make diamond the world's
most popular gemstone.
Diamonds are a bit of a mystery. They are composed of the element carbon and
because of that many people believe that they must have formed from
coal. Many teachers still teach this in their classrooms. But that is not true!
How Do Diamonds Form?
Diamonds are not native to
Earth's surface. Instead they form at high temperatures and
pressures that occur in Earth's mantle about 100 miles down.
 | How do diamonds form?
A detailed article that explains the four sources of diamonds found at Earth's surface. |
|
Most of the diamonds that have been discovered were delivered
to Earth's surface by deep-source volcanic eruptions. These eruptions
begin in the mantle and on their way up they tear out pieces of
mantle rock and deliver them to Earth's surface without melting.
These blocks from the mantle are known as xenoliths. They contain
diamonds that were formed at the high temperature and pressure conditions
of the mantle.
People produce diamonds by mining the rock that contains the
xenoliths or by mining the soils and sediments that formed as the
diamond-bearing rock weathered away.
Some diamonds are thought to form in the high temperature-pressure conditions of
subduction zones or asteroid impact sites. Some are delivered to earth
in meteorites.
No commercial diamond mines have been developed in deposits with these origins.
Did you know? Diamonds are mined in Canada and Arkansas
| Physical Properties of Diamond |
| Color |
Most industrial-grade diamond is black in color due to impurities. Gem diamond occurs in many colors, including: colorless, yellow, red, orange, green, blue, and brown. |
| Streak |
diamond is harder than a streak plate - when this occurs the streak is called "colorless" |
| Luster |
adamantine - the highest level of luster for a nonmetallic mineral |
| Diaphaneity |
transparent |
| Cleavage |
perfect, octahedral |
| Hardness |
10 - the hardest mineral |
| Specific Gravity |
3.5 - 3.6 |
| Distinguishing Characteristics |
hardness, heat conductivity, crystal form, index of refraction, dispersion |
| Chemical Composition |
C (elemental carbon) |
| Crystal System |
isometric |
Gem Diamonds vs. Industrial Diamonds
Gem diamonds are stones with color and clarity
that make them suitable for jewelry or investment use. These
stones are especially rare and make up a minor portion of worldwide
diamond production. Gemstone diamonds are sold for their beauty and quality.
Industrial diamonds are mostly used in cutting, grinding, drilling and polishing procedures. Here, hardness and heat conductivity characteristics are the qualities being purchased. Size and other measures of quality relevant to gemstones are not important. Industrial diamonds are often crushed to produce micron-sized abrasive powders. Large amounts of diamonds that are gemstone quality but too small to cut are sold into the industrial diamond trade.
Diamond as a Gemstone
Diamonds are the world's most popular gemstones. More money is
spent on diamonds than on all other gemstones combined. Part
of the reason for diamond's popularity is a result of its optical
properties - or how it reacts with light. Other factors include fashion, custom and marketing.
Diamond Consumption in the United States
In 2010 consumers in the United States spent about $19 billion on gemstones. Of that amount $18 billion was spent on diamonds and less than $1 billion was spent on colored stones. Diamonds are the most popular gemstones with U.S. consumers by a wide margin. |
Diamonds have a very high luster. The high luster is a result of
a diamond reflecting a high percentage of the light that strikes
its surface. This high luster is what gives diamonds their
pleasing "sparkle".
Diamond also has a high dispersion. As white light passes through a
diamond this high dispersion causes that light to separate into
its component colors. Dispersion is what enables a prism to separate
white light into the colors of the spectrum. This property of dispersion
is what gives diamonds their colorful "fire".
Diamond Gemstone Quality
The quality of a diamond gemstone is primarily determined by four
factors: color, cut, clarity and carats.
Color: Most gem quality diamonds range from colorless to yellow.
The most highly regarded stones are those that are completely
colorless. These are the ones sold for the highest prices.
However, another category of diamond gemstone is increasing in
popularity. These are the "fancy" diamonds, which occur in a variety
of colors including, red, pink, yellow, purple, blue and green.
The value of these stones is based upon their color intensity, rarity and
popularity.
Cut: The quality of workmanship in a diamond has a large
impact upon its quality. This influences not only the geometric appearance of
the stone but also the stone's luster and fire. Ideal stones are perfectly
polished to be highly reflective and emit a maximum amount of fire. The
faceted faces are equal in size and identical in shape. And, the edges of each
faceted face meet perfectly with each of its neighbors.
Clarity: The ideal diamond is free from internal flaws
and inclusions (particles of foreign material within the stone). These
detract from the appearance of the stone and interfere with the passage
of light through the stone. When present in large numbers or sizes they
can also reduce the strength of the stone.
Carat: Diamonds are sold by the carat (a unit of weight
equal to 1/5th of a gram or 1/142nd of an ounce). Small diamonds cost less per carat than larger stones of equal quality. This is because very
small stones are very common and large stones are especially rare.
Diamonds Used as an Abrasive
Because diamonds are very hard (ten on the Mohs scale) they are often used as an abrasive. Most
industrial diamonds are used for these purposes. Small particles of
diamond are embedded in a saw blade, a drill bit or a grinding wheel for
the purpose of cutting, drilling or grinding. They might also be ground
into a powder and made into a diamond paste that is used for polishing
or for very fine grinding.
There is a very large market for industrial diamonds. Demand for them exceeds
the supply obtained through mining. Synthetic diamonds are being produced to
meet this industrial demand. They can be produced at a low cost per carat and
perform well in industrial use.
Other Uses of Diamonds
Most industrial diamonds are used as abrasives. However, small amounts of
diamond are used in other applications.
Diamond windows are made from thin diamond membranes
and used to cover openings in lasers, x-ray machines and vacuum chambers.
They are transparent, very durable and resistant to heat and abrasion.
Diamond speaker domes
enhance the performance of high
quality speakers. Diamond is a very stiff material and when made into a
thin dome it can vibrate rapidly without the deformation that would
degrade sound quality.
Heat sinks are materials that absorb or transmit excess
heat. Diamond has the highest thermal conductivity of any material. It is
used to conduct heat away from the heat sensitive-parts of high performance
microelectronics.
Low friction microbearings are needed in tiny mechanical
devices. Just as some watches have jewel bearings in their movements
diamonds are used where extreme abrasion resistance and durability
are needed.
Wear-resistant parts can be produced by coating surfaces
with a thin coating of diamond. In this process, diamond is converted into
a vapor that deposits on the surface of parts prone to wear.
Synthetic Diamonds and Simulants
Diamond is a very valuable material and many people have worked to create synthetic diamonds and diamond simulants. Synthetic diamonds are man-made materials that have the same chemical composition, crystal structure and properties
as natural diamonds. Diamond simulants are materials that look like diamonds but have different
chemical compositions and physical properties.
The first commercially successful synthesis of diamond was accomplished in 1954 by workers at
General Electric. Since then, many companies have been successful at producing synthetic diamond
suitable for industrial use. Today, most of the industrial diamond consumed is synthetic with
China being the world leader with a production of over 4 billion carats per year.
In the last decade a few companies have developed technology that enables them to produce
gem-quality laboratory-created diamond up to a few carats in size in several colors. Some
companies are using high-pressure, high-temperature methods while others are using
chemical vapor deposition methods. Their stones are being sold in stores and on the internet
at a significant discount to natural stones of similar quality and size. These stones are
required to be sold with a disclosure that they are "synthetic" or "laboratory-created".
Contributor: Hobart King
More from Geology.com
| Sunstone: A feldspar with aventurescence caused by light reflecting from platy inclusions. |
| Rocks: Photos of igneous, sedimentary and metamorphic rocks. |
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| Minerals: The building blocks of our society. We use items made with minerals every day. |
| Volcanoes: Articles about volcanoes, volcanic hazards and eruptions past and present. |
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| A green diamond crystal. The color and cubic crystal shape are natural. Many natural diamond crystals are cubic or octahedral in shape. This diamond is about 4 millimeters across and is suitable for industrial use. |
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Estimated production levels for countries mining at least one million carats of gem-quality diamonds during calendar year 2010.
Graph by Geology.com. Data from USGS Mineral Commodity Summaries. Learn about the countries that produce diamonds. |
| A round, brilliant cut diamond showing "fire". © iStockphoto / Greg Stanfield |
A drill bit used in the drilling of oil wells. Each of the cutting tips has small grains of diamond embedded in the metal. These cut their way through the rock as the bit turns.
© iStockphoto / mikeuk |
| Small "fancy" diamonds in purple and canary yellow colors. Stones are about 4 millimeters across. |
| A demonstration of dispersion: white light being separated into its component colors while passing through a prism. Diamonds have a high dispersion. NASA Image. |
| A concrete saw with a diamond blade of about four feet diameter. US Air Force Image. |
| A natural, uncut octahedral diamond crystal. © iStockphoto / Timo Klein |
| Synthetic diamonds of various colors grown by the high-pressure high-temperature technique. Image by Wikipedia contributor Materialscientist. |
[1] Gemstones: Donald W. Olson, U.S. Geological Survey, Mineral Commodity Summaries, January 2012.
[2] Gemstones: Donald W. Olson, U.S. Geological Survey, 2009 Minerals Yearbook, July 2011.
[3] Diamond, Industrial: Donald W. Olson, U.S. Geological Survey, Mineral Commodity Summaries, January 2012.
[4] Diamond, Industrial: Donald W. Olson, U.S. Geological Survey, 2009 Minerals Yearbook, July 2011.
[5] The Nature of Diamonds: Exhibition Website, The American Museum of Natural History. Accessed, April, 2012.
[6] About the 4Cs: An explanation of how diamonds are evaluated. Gemological Society of America. January, 2010. |
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