Peggy Crossley, age 16, of Middletown, Ohio, for her question:
HOW ARE DIAMONDS JUDGED?
Diamond is the hardest naturally occurring substance known to man and is also one of the most valuable. Because of its hardness, the diamond is the most enduring of all gem stones. Diamonds are judged or graded according to weight, purity, color and cut.
The weight of a diamond is measured by a unit of weight called a carat. One carat weighs 200 milligrams. The largest diamond ever discovered was the Cullinan which was found in the Premier mine of South Africa in 1905. It weighed 3,106 carats or about one and a half pounds.
The purity of a diamond can be lessened by various kinds of flaws. These flaws include the presence of foreign material, small bubbles and small cracks or fissures which jewelers sometimes call feathers.
The color of most diamonds used in jewelry consists of a faintly yellowish tint. A small percentage of gem diamonds are colorless and a few posess a faint tinge of blue. There are also red, yellow, brown, green and even black diamonds, although only yellow and brown diamonds are common.
The cut of the diamond affects its value because a stone that is not properly proportioned does not have as much brilliance as a stone that is well cut.
A flawless diamond should have no physical defects, such as cracks, spots, scratches, blemishes or cloudy texture. But a flawless diamond may not have the right color. Some dealers restrict the term "perfect" to describe a diamond that has no flaws and is also the right color and cut.
Cutting and polishing the rough diamond is a slow and costly process. It must be done by highly trained workers who take many years to learn to do their work skillfully.
About 80 percent of the world's diamonds are suitable only for industrial use.
Diamonds are crystals formed almost entirely of carbon. Most diamonds have eight sides which form a double pyramid. Some diamonds have as many as 12 sides while others have six sides, forming a cube.
Scientists believe that diamonds were formed millions of years ago when carbon was subjected to great heat and pressure.
A diamond must be used to cut another diamond. But a diamond can be separated or broken with a severe blow because of its cleavage. Cleavage is a property some minerals have of splitting in certain directions and producing flat, even surfaces.
A diamond will not dissolve in acid. But it can be destroyed when it is subjected to intense heat. If a diamond is heated in the presence of oxygen, it will burn and form carbon dioxide. If it is heated without oxygen, it will turn to graphite, a mineral so soft that it is used as a lubricant.