“And the second row shall be an emerald, a sapphire, and a diamond”; ”Thou hast been in Eden the garden of God; every precious stone was thy covering, the sardius, topaz, and the diamond . . .”; “The sin of Judah is written with a
pen of iron, and with the point of a diamond: it is graven upon the table of their heart, and upon the horns of your alters”—Exodus 28:18; Ezekial 28:13; Jeremiah 17:1. So says the Bible concerning diamond. The Exodus reference assigns 12 precious stones, including diamond, to be set in a breastplate worn by Aaron the high-priest. Each precious stone represents one of the 12 tribes of Israel.
The Ezekial lamentation affirms the precious nature of diamond, and the Jeremiah symbolism asserts that the sins of Judah were very bad and that diamond is very hard. The words of Jeremiah are the first known mention of an industrial use for diamond; namely, a scribing tool capable of writing on all other solid materials. It is thought that diamonds of biblical times came from India, probably Golconda in Cashmere. However, diamond mining as an industry in India probably did not begin until about 700 B.C. The second source of diamonds is thought to have been discovered in Borneo about A.D. 600. Following this, diamonds were discovered in Brazil in 1726 and South Africa in 1867. Since that time, diamonds have been found in many places in Africa, and that continent remains to this day the world’s principal supplier. Since World War II, diamonds have been mined in the Soviet Union. Diamonds were mined in the United States for a short time in Pike County, Arkansas, about the time of World War I. Recently, diamonds have been discovered along the Wyoming Colorado border in the United States, but the extent of the deposit is not yet known.
The diamonds of India and Brazil and some of the deposits of Africa are alluvial. But the original source of diamonds is volcanic in nature. Hot lava of a peculiar nature had, in many parts of Africa, the USSR, and the United States, worked its way upward from great depths to the earth’s surface. The resultant “pipes” of solidified lava contain a complex material known as “blue ground” and this is mined by underground tunneling. The diamond content is very low. Only one carat (ct) of gem quality diamond is obtained from 320,000,000 ct of blue ground. However, 3.5 ct of industrial diamond is found along with the single carat of gem diamond. The geology of the pipes has been extensively studied. However, the manner in which the diamonds were formed in them is not known.
The pipes offered no clues for the method by which diamonds were finally synthesized in the laboratory. The word carat comes from the carob bean which was used as a comparison of weight by the early diamond merchants of India. The exact weight of the carat has varied somewhat down through the ages, but is set today as being exactly equal to 0.2000 g. The first extensive use of diamond in industry was as diamond powder mixed with olive oil. This abrasive slurry was placed on the horizontal face of a spinning cast iron plate to polish rough diamonds (held under pressure against the face) into faceted gems.
The beginnings of this art are lost to history but probably started about A.D. 1500. In the year 1927 a new, hard engineering material known as cemented tungsten carbide was introduced to the world. In this, micron sized tungsten carbide particles are sintered together with cobalt powder to form a shape of the approximately desired dimensions. This rough shape is then ground to the precisely desired shape with diamond grinding wheels. A very important example of a diamond ground shape is the indexable tungsten carbide cutting tool insert.
Throw-away inserts of triangular, square, and other shapes are used by the millions in various machine tools such as lathes and milling machines. A major use of industrial diamond today is in the grinding and finishing of various cemented tungsten carbide parts and cutting tools. As the tungsten carbide industry has expanded (growth has been remarkable since its introduction), the growth of the diamond wheel market has correspondingly increased. In 1935, only about half of all diamonds mined were used in industry. Now, this figure has increased to about 80%. Before introducing the subject of industrial synthetic diamond and the methods for its production, it is appropriate to acquaint the reader with some of the properties of diamond.
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