Sec. II, Ch. 1: The Diamond

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	SECTION II.

	CHAPTER I. THE DIAMOND.

	IAMONDS, as they occur in Nature, usually but not invariably present the form of crystals, more or less regular and perfect in their development. These forms belong to the group of geometrical solids known to crystallographers as the Cubic or Tesserai or Isometric system. The most common forms are the regular octahedron and the rhombic dodecahedron ; the former bounded by eight equilateral triangles, and the latter by twelve rhombs, or lozenge-shaped surfaces. It is notable that the faces of the crystals are often more or less curved, or convex, whilst those of other crystalline bodies, with few exceptions, are flat. Not unfrequently the Diamond takes the form of a six-faced octahedron, which, by the rounding of its eight-and-forty faces becomes almost spherical or approaches a small ball in shape. In some cases the crystals are curiously " twinned " or " macled." Groups of crystals, dodecahedra as well as octahedra, are not rare ; there is for instance, a very fine specimen of such a mass of coalesced octahedra in the Royal Mineral Museum at Dresden. In the Vienna Collection there is a Diamond which has, enclosed within itself, another similarly-crystallised Diamond of a yellow-colour ; and

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