The first rough shaping of the more important facets of the brilliants is here seen performed by the workman, who operates on two diamonds at once, by bruising each against the other, angle against angle. The dust that falls from the stones is preserved for the subsequent processes of grinding and polishing those facets that distinguish the many-sided brilliant from the dull, original crystal of the diamond. It is used, mingled with oil, on a flat iron disk, set revolving with vast rapidity by steam-power, the stone itself being held upon this disk or wheel by a tool to which it is attached by a mass of fusible metallic alloy, into which the stone is skilfully inserted. Skill of eye and hand, only attainable by great practice, is needed for this work; but a skill not less exact is needed for another process, which may here be seen in daily operation--the process of cleavage. The diamond, when a blow is struck on an edged tool placed parallel to one of the octahedral faces of the crystal, readily splits in that direction. But to recognize the precise direction on the complex and generally rounded form of the diamond crystal; to cut a little notch by means of a knife edge of diamonds formed of one of the slices cleaved from a crystal, and to cut that notch exactly the right spot; then to plant the steel knife that is to split the diamond precisely in the right position; finally, with a smart blow, to effect the cleavage so as to separate neither too large nor small a portion of the stone--these various steps in the process need great skill and judgment, and present to the observer the interesting spectacle which a handicraft dependent on experience of hand and eye always affords. But Mr. Coster’s exhibition has other objects of interest. For the first time, we may see here, side by side, the diamond with the minerals that accompany it in the river beds of Brazil; and there are even examples in which crystals of diamonds are included within a mass of quartz crystals, which have all the appearance of having been formed simultaneously with deposits of the diamond. The different districts of Rio and of Bahia are thus represented--the former producing a confusedly crystallized sort of diamond termed “bort,” and the latter an opaque black variety; both these kinds being found associated with the crystallized diamonds used for jewelry. Though useful in state of powder, the black carbon and “bort” are incapable of being cut as a jewel.--_“Maskelyne’s Report,” Great Exhibition._ The Alloys of Aluminum with Copper.