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FIRE IN THE EARTH
Boart is an imperfectly crystallized diamond, a con­glomeration of minute crystals of diamond having no clear portions and no planes of cleavage and therefore useless as a gem. Exceptionally hard, when crushed it provides the diamond powder used in cutting and polishing other dia­monds. In practice it has become a generic trade term to indicate any class of diamond (including fragments) not of sufficient commercial value to be used otherwise than for crushing. It is reduced to powder by pounding in a steel mortar.
There are a number of kinds of boart. There is common boart, which varies in structure from very fine-grained to a coarse-grained crystalline aggregate of all shapes and sizes and colors ranging from gray to gray-black and black. There is stewartite boart or magnetic, so named because James Stewart, manager for years of De Beers concentrating plant, noticed that some varieties of boart were removed by the magnetic separator which in the ordinary course should have formed part of the non-magnetic residue. Samples of these diamonds were submitted to experts who confirmed the fact that they were magnetic. The color is the same as any other boart, the hardness the same as any ordinary diamond.
There is hailstone boart, a name used for a particular type of diamond which differs greatly in appearance and struc­ture from all other forms of boart. The color (it is of a cement-looking material) is generally gray to gray-black and the hardness less than either the ordinary diamond or com­mon boart.
There is framesite boart, named after the chairman of the Premier mine, Mr. P. Ross Frames, but it is in no way different from what is generally referred to as common boart The tiny particles making up the whole aggregate are so
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