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generally available plan will be to follow a classification according to colour. For as the ornamental or artistic employment of precious stones conveys primarily, if not wholly and ultimately, an appeal to the eye, it is clear that such optical properties as can be comprised in the terms lustre, light, and especially colour, should be our first consideration. After all, as, on the whole, the prominent feature of precious stones is their colour, so the easiest way of considering their colour is to adopt the order of succession of the colours in the ordinary rainbow or prismatic spectrum, beginning with the white light, which contains them all, and originates them all.

White Stones.—The diamond naturally takes the first position if we consider its hardness, its remarkable composition, and its strong refraction and dispersion of light. Its properties, so far as they appeal to the eye, differ much from those belonging to the majority of other stones, and it forms, partly in consequence of this peculiarity, as good a border or setting to other gems as a gold frame generally does to a picture. Of course much depends upon the quality of the diamond, and much upon the shape which is given to it by the lapidary. The flat plates of lasque diamonds, and, in less degree, the step-cut stones with broad tables, exhibit the unique and splendid lustre which is peculiar to the polished surface of this stone; these forms also permit the transparency and the total internal reflection of light to be well seen. Even the form of the diamond crystal, the regular octohedron, when its surfaces are really planes, well exhibits the transparency and reflection of the stone. Next to the diamond we may place the colourless zircon or jargoon, then the phenakite, then the white sapphire, the white topaz, and the white beryl. Rock crystal will come below these in point of beauty and brilliancy. The colourless zircon sometimes approaches near in prismatic brilliancy to a diamond; so, at night especially, does the rare and curious mineral phenakite. There is, however, always a sort of difficulty in finding