2. Tourmaline (some specimens of which perhaps more nearly approach the emerald than any other green stones). 3. The demantoid garnet (sometimes called "olivine" in the trade). 4. True olivine (the peridot and the chrysolite of the trade). 5. Bluish-green beryl (aquamarine). 6. Green sapphire (Oriental emerald or Oriental aquamarine). 7. Chrysoberyl (alexandrite and also the greenish-yellow chrysoberyl). 1. Considering first the emerald, we have as legitimate a use of color in distinguishing a stone as could be selected, for emerald of fine grass-green color is not equaled by any other precious stone in the rich velvety character of its color. We have to beware here, however, of the fine glass imitations, which, while lacking the variety of true emerald, because of lack of dichroism, are nevertheless of a color so nearly like that of the emerald that no one should attempt to decide by color alone as to whether a stone is genuine or imitation emerald. If a hardness test shows that the material is a genuine hard stone and not a paste, then one who is well accustomed to the color of fine emerald can say at once whether a stone is a fine emerald or some other hard green stone. Where the color is less fine, however, one might well refuse to decide by the color, even when sure that the material is not glass, for some fine tourmalines approach some of the poorer emeralds in richness of color. THE "SCIENTIFIC EMERALD" FRAUD. No "scientific" emeralds of marketable size have ever been produced as far as can be learned. Many attempts to reproduce emerald by melting beryl or emerald of inferior color have resulted only in the production of a beryl glass, which, while its color might be of desirable shade, was softer and lighter in weight than true emerald. It was also a true glass and hence singly refracting and without dichroism, whereas emerald is crystalline (not glassy or amorphous), is doubly refracting, and shows dichroism. Do not be misled, then, into buying or selling an imitation of emerald under the terms "synthetic," "scientific," or "reconstructed," as such terms, when so used, are used to deceive one into thinking that the product offered bears the same relation to the true emerald that scientific rubies and sapphires bear to the natural stones. Such is not the case. About the most dangerous imitation of the emerald that is ever seen in the trade is the triplet that has a top and a back made of true but pale beryl (the same mineral as emerald, but not of the right color) and a thin slice of deep emerald green glass laid between. This slice of glass is usually placed behind the girdle so that a file will not find any point of attack. The specific gravity of the triplet is practically that of emerald, its color is often very good, and it is doubly refracting. It is thus a dangerous imitation. (See Fig. 8.)