Science And Environment: How Diamonds Work

Diamonds are valuable both for their beauty as a gem, and for their hardness, which makes them useful in industry.

Diamonds are one of the most valuable minerals on earth. While usually depicted as brilliant white, they actually can be found in different colors. South Africa is a leading producer of diamonds, but they are also found across most of North America, in Eastern Europe, Northern Russia, and even in various spots on South America and Australia. They are beautiful symbols of lasting love and prosperity. But what is it about diamonds that makes them so unique and valuable?

Diamonds are usually found in "pipes," vertical tubes from extinct volcanoes, which raise diamonds from the earth's mantle. As rain erodes the soil around these pipes, the diamonds are exposed, and washed downhill, eventually to rivers and the sea. Diamonds can be mined either from the pipes themselves, or from rivers and seas.

When mined from the ground, the rock in the pipes must be crushed in order to reveal the diamonds. In alluvial mining, which is done in rivers, the gravel at the bottom of the moving water is examined for diamonds that have been deposited there. Mining can also be done in the sea, looking for deposits of diamonds on the coastal sea floor. These diamonds are usually of very high quality, because they have survived much erosion and movement.

After mining, the stones are sorted and graded. Diamonds are graded for value according to four categories, which all begin with "c." "Carat" refers to the weight of the diamond. A carat equals 1/5 of a gram. The value of a diamond increases exponentially with size. Several small diamonds that equal a carat in weight are not worth as much as a single 1-carat stone, which can easily cost $5000 or more.

"Clarity" means how clear the gem is. Does it contain mineral imperfections? These lower the value of the stone. "Color" in diamonds is usually white to cream, with the whiter stones being more valuable. Some diamonds, known as "fancies," have distinct color, and are valued according to the rarity and quality of the color. And the "cut" of the diamond, the skill with which the gem cutter has shaped it, is the final factor in determining the value of a diamond.

The standard cut for a diamond is called the "brilliant." A gem cutter named Marcel Tolkowsky, who was also an engineering student, developed the cut in 1911, based on mathematical principles. The brilliant cut has 58 facets, which bring out a diamond's fire, reflecting and refracting light rays. One reason people love diamonds is their ability to refract light into all the different colors of the rainbow. This is known as a diamond's "fire."

Other popular cuts are the oval, the marquis, and the emerald. It takes many hours to cut a diamond properly. If a diamond is not cut well, it will not refract light from the sides and bottom, and thus will not have the desired "fire."

Diamond is the hardest material known. For this reason, most of what is mined, as much as 80%, is used in industry. Since they are so hard, they are used to make saws and sanding devices for other hard materials, such as rock, gems, glass, and metal. Diamond polishing pads are used to polish granite, marble and concrete surfaces. They are also used in machines designed to sharpen ice skates.

Diamond tools can be damaged easily, so rubber and plastic caps are available to cover their cutting edges. High speeds are easier on the saw blade edges than lower speeds. The blade should not be stationary when it comes into contact with the material that is being cut.

Diamonds are hard because of their molecular bonds. In 1796, an English scientist named Smithson Tennant discovered that diamond is comprised of only carbon atoms, bonded to each other in the strongest possible configuration. Interestingly, graphite, commonly called "pencil lead," is also made up of only carbon atoms. The difference in these two minerals is entirely in the chemical bond between the atoms.

Carbon has an atomic number of 6, which means each atom has 4 electrons in its outer shell. Most atoms seek to have 8 electrons in their outer shell, which causes them to share electrons with each other. This is what leads to chemical bonds. Since carbon atoms have 4, they are able to share all 4 electrons with their neighboring atoms, which in turn share with them. When these bonds are arranged on a plane, the result is thin sheets of carbon that slip off each other. This describes graphite, and why it can be used as a lubricant, and how the thin sheets rub off the pencil onto the paper.

When these 4 outer electrons are shared among carbon atoms in a 3-dimensional form (in the shape of a tetrahedron), they form an intricate interlocking system of bonds. This accounts for the hardness of diamond. These bonds form under intense pressure, as is found in volcanic activity.

Since diamonds are so desirable, yet so expensive, scientists sought for many years to find a way to create artificial ones in the lab. These are often called faux diamonds. One well known type of these is cubic zirconium. Genuine diamonds rate a 10 (the highest) on the Mohs hardness scale for minerals. Good quality CZ stones can rate a 9. A 1-carat CZ diamond costs between $50 and $100.

For an interesting family vacation in the U.S., try Crater of Diamonds State Park, in Murfreesboro, Arkansas. Here, for a fee, you can hunt for diamonds in a 37 acre plowed field that contains the eroded surface of an extinct volcano pipe. And you may keep any you find. Park rangers estimate that an average of 2 small diamonds are found daily, and occasionally a large one can still be found.

Over 75,000 diamonds have been found in this field since 1906. It's thought to be one of the top ten diamond mines in the world. The name "Arkansas diamond," however, often refers to locally found quartz.

Diamonds are a unique natural resource. Valued for both their beauty and usefulness, they are truly a treasure.

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