Diamond is the best known gem. It is known as the king of gems for its brilliance and for being the hardest mineral on earth. (Foa, p.50) Its characteristics enable it to be used for many different purposes. Since diamonds are the hardest gems on Mohs scale, they make useful tools for industrial purposes, such as drilling hard materials. However, they are quite rare, which makes them very valuable. Their beauty and brilliance make them perfect for jewelry.
Diamond is made up of carbon. Another form of pure carbon is graphite. Graphite is the stable form of carbon, found at the earth s surface. Despite the fact that they have identical chemical composition, the two minerals are drastically different. Diamond is the hardest known substance and is usually light colored and transparent, while graphite is greasy, easily powdered, and very dark in color. Diamond is the hardest gem on Mohs hardness scale and graphite is the softest. Diamond is very hard because of its dense packing and interlocking atomic arrangement. Graphite, on the other hand, although it is the same element, is more loosely packed and has a six-sided, layered configuration, which makes it soft (Pough, 1991). The differences between graphite and diamonds are accounted for by the conditions in which they are created.
Diamonds form over long periods of time, between 100 km and 200 km below the surface. At this great depth, carbon gets a chance to cool very gradually, forming diamond crystals. When volcanic eruptions occur, magma carries the diamonds up to the surface of the earth. Kimberlite lavas carrying diamonds erupt at anywhere between 10 and 30 km/hour and increase their velocity to several hundred km/hour within the last few kilometers. (Pough, 44) At the surface, this lava cools and turns into Kimberlite rock. That is why diamonds are often found in kimberlite, a volcanic rock, which is often much younger than the diamonds themselves. All diamonds that are around today are at least 990,000,000 years old. If the same element carbon found its way to the surface, before it got a chance to form crystals and solidify, it would turn into graphite.
Diamond crystals occur in a variety of shapes and forms. There are octahedral, cubic, and dodecahedral diamond crystals. The octahedral crystals are formed with eight sides, the cubic ones have six sides, and the dodecahedral crystals have 12 sides. Of these, the octahedral crystals are the most common. Occasionally, crystals are found where three smaller faces have replaced each face of the octahedron, so that the crystal becomes 24-sided. (Fisher, p.52) Some rough diamond crystals contain a combination of these forms. This is an especially common occurrence in Brazil, where diamonds are sometimes found in which many tiny crystals are tightly packed together. These kinds of diamonds, which grow in bunches are called carbonados. (Fisher, p.52) Carbonados are usually used in industry. Diamonds are very important in industry because they are used for the manufacture and use of various precision instruments. These instruments are employed in grinding and polishing glass, polishing ceramics, stones, etc. Diamond drill crowns are used in the oil mining industry to drill through the earth to the oil.
There are many different legends and beliefs associated with diamonds. For example, the Hindus believed that a flawed diamond would bring misfortune, while the Greeks thought that diamonds could protect against poison. (Foa, p.50)
The value of a diamond depends on four primary factors. These are (1) color, (2) clarity, (3) cut, and (4) carat weight. A diamond cutter or jeweler determines the color of a diamond by comparing it visually with "knowns," or the diamonds for which the color has already been determined. For example, in "colorless" or not "fancy" stones, the value of the stone goes down with increasing yellow. However, once the color content reaches the point where the stone is considered a fancy stone, it becomes very expensive.
The most familiar diamonds are white or colorless, usually with a tinge of yellow or gray. However, diamonds come in a wide variety of colors. There are golden yellow, pink, brown, and green diamonds, just to name a few of the possibilities. Richly colored stones are called fancies and are very rare and expensive. Fancy colors include pink, green, blue, amber, and golden-yellow. The various colors of diamonds are due to impurities in them. For example, traces of nitrogen give brown, yellow, green, and black stones. Blue diamonds owe their color to the presence of boron in them. (Foa, p.51) Some of the most famous diamonds in the world are colored diamonds, such as the Dresden green, which weighs 48.5 carats and the Hope Diamond, which is 44.5 carats.
The clarity of the stone is determined by the amount of blemishes or flaws, scratches, nicks, and "naturals" in the stone. "Naturals" is the original surface of an uncut stone. There are a number of systems of nomenclature for expressing the clarity of a stone. All of these systems are based on placing the stone into a relative category, which range from flawless to imperfect.
The cut of the stone also plays a big role in the stone s appearance and is thus one of the determining factors in the value of the diamond. Facets are placed on the stone so as to maximize its brilliance. For example, placing facets on the crown of a diamond takes advantage of the prism effect, making the person looking at the diamond see rainbows and glints of color. The cut of the stone is ranked from very good to poor.
Although they are very hard, diamonds cleave easily, which means that they are very brittle. They cleave in only one structural direction known as the direction of octahedral face. (Arem, p.32) In this direction, the crystal lattice appears to consist of parallel planes that are spaced at relatively wide distances from one another. Diamond crystals may sometimes be very symmetrical, but they are not as shiny and transparent as cut and faceted stones. In faceted stones, light particles become trapped inside the stone and are bounced around between the facets, making the diamond sparkle. (Arem, p.35)
Finally, the carat weight of the diamond is very significant. The carat weight is determined by weighing the stone. A diamond that weighs 0.2g is said to be one carat. The greater the carat weight of the stone, the greater its value.
Diamonds are mined all over the world. The world s oldest major source of diamonds is India. For centuries, it has supplied stones to all parts of the globe. (Arem, p.34) Gradually, new places for mining were discovered. Today, there are diamond mines in Brazil, Venezuela, Guyana, Australia, etc. Despite this abundance in places where mining takes place, high quality diamonds are not abundant at all. On the average, a diamond mine yields less than one carat of diamond for every five tons of rock. Of this, on average, less than 20% is usable for gems and half of this is lost in cutting. (Arem, p.37)
In order to be used in jewelry, after diamonds are mined, they must be cut. Because diamonds have such a high hardness, they are cut using other diamonds. What allows them to be cut at all is the fact that they do not have uniform harness throughout the entire stone. For example, the point of an octahedron is harder than the surface of an octahedral face. Therefore, when powdered diamond is used to cut a diamond crystal, the powder will always contain some particles that are oriented in a hard direction in relation to the crystal being cut. (Arem, p.38)
Arem, Joel E. All-Color Guide: Gems and Jewelry. 2nd edition. Geoscience Press, Inc.
Fisher, P. J. The Science of Gems. Charles Scribner s Sons. New York, 1966.
Foa, Emma. Pockets Gemstones. DK Publishing. New York, 1997.Pough, Frederick H.
Peterson Guide to Rocks and Minerals. Houghton Mifflin Company.