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!

Diamond Crystal

Occurrence of Diamond

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.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.

Physical Properties

Physical Properties of Diamond

Chemical Classification Native element
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
Mohs Hardness 10 - the hardest mineral
Specific Gravity 3.4 to 3.6
Diagnostic Properties Hardness, heat conductivity, crystal form, index of refraction, dispersion
Chemical Composition C (elemental carbon)
Crystal System Isometric
Uses Gemstones, industrial abrasives

Gem Diamond 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.
Natural diamond crystals have a specific gravity that ranges between approximately 3.4 to 3.6. This range exists because most diamonds contain impurities and have irregularities in their crystal structure. Gem quality diamonds are the most perfect diamonds, with minimal impurities and defects. They have a specific gravity that is very close to 3.52.

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.

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 are 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.

Sources: Geology.com

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