DIAMOND, a natural form of carbon, highly valued as a precious stone when trans parent and of the crystalline form. The dia mond crystallizes in the cubic or monometric system, its common form being the regular octahedron or a modification of it. The faces are often curved and the general form of the crystal is more or less rounded. The surface of the diamond frequently exhibits stria: and triangular impressions, while the interior may contain microscopic cavities and various in clusions, often black carbon. It is the hardest substance known, but is cleavable; specific gravity, 3.52. It is generally colorless, but sometimes tinged with yellovv, pink, red, orange, green, blue, brown or blade. Blue, red and green are exceedingly rare colors. The finest deep red diamond known is that in the posses sion of the Russian Crown, purchased in the time of the Emperor Paul of Russia. Light yellow, straw and brown are the most common colors; rich yellow and browns are also highly prized. Some bluish white Brazilian diamonds are phosphorescent in the dark after exposure to the sunlight. The color is attributed to the presence of a possible hydrocarbon, called Tiffanyite. This phos phorescence is a property peculiar also to alizarin. Exposed to the Roentgen or X-ray the diamond is transparent when radiographed, imitation diamonds appearing opaque. The diamond phosphoresces when exposed to roentgen rays, polonium or radium, retaining the light for some time. The brilliancy of the gem is caused by the planes reflecting all the light that strikes them at an angle exceed ing 24 degrees 13 minutes. The index of refraction is 2.439, being exceeded only by that in chromate of lead and orpiment. The diamond is unaffected by any liquid and infusible at the highest attainable temperature. It gradually burns away at from 760° to 875° C., according to hardness, before the oxy-hydro gen blowpipe, or when heated and plunged into an atmosphere of oxygen, carbonic acid then being produced. Exposed to the intense heat of the voltaic arc, the diamond becomes converted into graphite at 3600° centigrade. Besides its value as a gem it is of great use in the arts and manufactures. Diamond dust is used for
polishing other gems, for slicing gems of all kinds, agate, jade and other hard substances. A crystal with natural rounded edges is used by glaziers for cutting glass, for engraving glass, steel and other substances; the cut is generally to a depth of only 1-100 of an inch, but determines the direction in which the glass shall break; a cut of this depth, while scarcely showing, breaks well, whereas a deep scratch does not. Natural fragments or splinters or cleavages, either with the natural edge or sharpened to a point are used for engraving on glass and other hard substances; a splinter is also used as a tool for turn ing glass lenses in a lathe; and rough diamonds, too imperfect to be used as gems, are mounted as boring tools for perforat ing the softer rocks. The amorphous black variety, the carbon, carbonado, or bort, is used for boring hard rocks. Rock to the depth of a mile has been bored with this material. It sells for $90 a carat, the value per carat of a fine transparent rough diamond of from one to two carats, as often only to 40 per cent of the crystal is left in the gem after the operation of cutting.
The finest old East Indian, the fontein, the Rivers and the blue Wesselton monds are all of approximately one grade. The finest Jagers and the finest River diamonds are known as uextra-jagers° and "extra Rivers)) respectively. The Wesselton is the quality superior to a fine "Cape.° The stals, or fine Capes, as they are called, are of the first quality and always have a fine tint. The Silver Capes have a yellowish tint, while the Bywaters have a decided yellow tint. When the color is pure and rich yellow, it is known as "fancy yellow.° Diamonds from the Premier mine occasionally have the faint ness or cloudiness of the Brazilian diamonds. Bultfontein diamonds are steel in color and occasionally contain minute black carbon spots. No whiter diamonds were ever found, even in India, than are now found in the Jagersfontein, • the Wesselton and Bultfontein mines.