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Glossary

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De Beers Consolidated Mines, L
This company is the major factor in the diamond industry, because it holds a controlling interest in a number of diamond-mining companies and in companies having buying contracts with independent producers. It owns or controls all of the important pipe mines in South Africa and Consolidated Diamond Mines of South-West Africa, Ltd. Williamson Diamonds, in Tanzania, is owned by De Beers and the government of that country on an equal basis.
Depth Percentage
The depth of a stone measured from the table to the culet, expressed as a percentage of the stone’s diameter at the girdle, is a relationship used in the analysis of the proportions of a fashioned diamond.
Diamantiferous
Diamond-bearing ground.
Diamond
A mineral composed essentially of carbon that crystallizes in the “cubic,” or “isometric,” crystal system and is therefore singly refractive. IT is by far the hardest of all known natural substances (10 on Mohs’ scale); only manmade Borazon and synthetic diamond are as hard. In its transparent form, it is the most cherished and among the most highly valued gemstones. It occurs in colors ranging from colorless to yellow, brown, orange, green, blue, and violet. Reddish stones are known, but those of an intense red color approaching that of ruby are excessively rare. Its hardness and high refractive index (2.417) permits it to be fashioned as the most brilliant of all gems, and its dispersion (.044) produces a high degree of fire. The specific gravity is 3.52. Sources include various sections of south, west, southwest and middle Africa; Russia; central, east and northeast South America; India; Borneo; and Australia. It is also found in the United State, but not in commercial quantity.
Diamond Certificate
A certificate awarded to those who complete successfully the “Diamond Course” of the Gemological Institute of America, which requires passing the diamond-grading and diamond-appraising instruction and practice.
Diamond Cut
A name sometimes used in the colored-stone trade for brilliant cut.
Diamond Saw
(a) A saw used for dividing or separating diamonds. (b) A diamond-charged blade used as a cutting edge in fashioning colored stones or in various applications in industry.
Diamond Syndicate
In the early days of South African diamond fields, the word “syndicate” was used to refer to various groups of individuals and companies that held controlling interests in diamond production and distribution. In 1890, a syndicate consisting of ten firms offered to produce all of De Beers Company’s diamonds. This seems to have been the embryo of the famous diamond syndicate that became so well known to jewelers in the early part of the 20th century as the price-fixing and market-controlling factor of the diamond industry. In various forms, a diamond syndicate composed of different persons or firms functioned in this capacity, until the crisis of 1929 demanded a marketing organization of a more rigid kind with greater capital. Although the term syndicate is no longer meaningful, it is often applied to De Beers Consolidated Mines, Ltd., because it holds a controlling interesting in a number of diamond-mining companies and in companies that have buying contract with independent producers, including the Diamond Corporation, Ltd.
Diamond Trading Co., Ltd
The organization that markets to the diamond industry the gem diamond it buys from the Diamond Purchasing & Trading Co., Ltd.
Dispersion
The property of transparent gemstones to separate white light into the colors of the spectrum. The interval between such colors varies in different gemstones, but in practice it is measure by the difference between the refractive indices of the red and blue rays. Diamond has the highest dispersion (.044) of any natural, colorless gem.
Dodecahedron
One of the seven basic forms in the highest symmetry (“hexoctahedral”) class of the cubic, or isometric, crystal system. It has 12 rhomb-shaped faces, each of which intersects two of the crystallographic axes and is parallel to the third. This form is uncommon in gem diamonds.
Draw Color
When several diamonds are placed together in a diamond paper and light passes through one stone after another, each stone tends to intensify the slight color of the other. The group of stones is then said to draw color. The term is also used to describe an individual diamond with a visible body color.
Durability
The durability of a gem depends both on its hardness and “toughness.” It may be quite tough but easily scratched, or it may be exceedingly hard but lack toughness because of easy cleavage. Diamond is highest on the scale of hardness and, despite it rather easily developed octahedral cleavage, it is among the toughest of gemstones.


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