The Diamond

8 Pages 2100 Words

face or surface varies with the direction of the cut.
Diamond crystalizes in the isometric system. Octahedra and rhombic dodecahedra are the crystal forms most commonly found, but cubes and other forms also occur. Rounded, distorted, and twinned crystals are also common. Crystalline diamonds always cleave cleanly along planes parallel to the faces of an octahedron. The specific gravity of diamonds ranges between 3.15 and 3.53, but the value for pure crystals is almost always 3.52.
Diamonds exhibit a wide range of transparency and color. Good quality diamonds of clear, strong, and unusual color are highly prized. Colorless stones, known as white diamonds, are extremely valuable, while yellow or brown tinged stones are regarded as imperfect. Green and blue diamonds are rarities and red diamonds are the rarest of all. Color in diamonds is caused by the presence of minor elements.
Two important characteristics of the diamond when used as a gem are its brilliancy and fire. Both the index of refraction and the dispersion (the physical properties that determine luster and fire) are higher for diamond than for any other natural, transparent, colorless stone. Uncut diamonds have a greasy luster and are not brilliant, but when cut the same stones exhibit a high luster, characterized technically as adamantine. The effect of the high dispersion is to separate the colored components of white light so that the stone sparkles when properly cut. Some diamonds exhibit fluorescence when exposed to sunlight or other ultraviolet-light sources. The color usually is light blue, but yellow, orange, milky white, and red fluorescence may occur in some stones.
Other characteristics of the diamond add nothing to its appearance but are frequently useful in identifying the stone and in differentiat...