318 SYSTEMATIC DESCRIPTION OF PRECIOUS STONES 



several green stones; thus "oriental emerald" is green corundum; " lithia-emerald " is 

 hiddenite, a green mineral belonging to the pyroxene group and found with the true 

 emerald in North Carolina; "emerald-copper" is dioptase, a beautiful green silicate of 

 coj)per. The t«o latter are both used as precious stones. 



The green minerals which are sometimes substituted for the emerald, and which may 

 be mistaken for it, include green corundum, known as " oriental emerald," green garnet, 

 known as demantoid, hiddenite, diopside, alexandrite, green tourmaline, and perhaps also 

 chrysolite and dioptase. Each of these minerals has a higher specific gravity than the 

 emerald ; each sinks in liquid No. 3, and some even in the heaviest liquid, while the 

 emerald floats in both. Moreover, the " oriental emei'ald " is much harder ; the demantoid, 

 the colour of which has usually a yellowish tinge though sometimes very similar to that of 

 the emerald, is singly refracting. Hiddenite is very rare, and is considered to be more 

 valuable than the emerald ; it is used as a gem practically in America only. Uiopside is 

 much more of a bottle-green colour than is the emerald. Alexandrite is distinguished 

 from emerald by its hardness and its remarkable dichroism. The colour of green 

 tourmaline, though often not dissimilar to that of pale emeralds, is frequently distinctly 

 bluish in character ; this mineral is easily distinguished from emerald, however, by its 

 specific gra^•ity, which is 3"07, slightly greater than that of liquid No. 3, in which, therefore, 

 it sinks. Chrysolite is yellowish-green, and can be distinguished from emerald by its colour 

 and its faint dichroism. Finally dioptase is always of a very dark emerald-green colour; it 

 is only semi-transparent and far softer than the emerald. A more detailed account of the 

 characters by which the emerald may be distinguished from other green stones which 

 resemble it more or less in appearance is given in Table 14, Part III. of this book. 



A glass of a fine emerald-green colour may be obtained by fusing together 4608 parts 

 of strass, 42 parts of pure copper oxide (CuO), and 2 parts of chromic oxide. It differs 

 from emerald in being optically isotropic, in the absence of any trace of dichroism, and in 

 being much softer. An imitation of emerald which contains from 7 to 8 per cent, of 

 beryllia is sometimes put on the market at the present time. It has a fine emerald-green 

 colour, but is not perfectly transpaj-ent ; it encloses numerous small air-bubbles and is not 

 dichroic ; its specific gravity is 3"19. It is obvious that we have here a glass to which 

 beryllia has been added in order to give it a chemical composition similar to that of true 

 emerald. 



PRECIOUS BERYL. 

 AQUAMARINE, "AQUAMARINE-CHRYSOLITE," AND GOLDEN BERYL. 



There are several colour-varieties of transparent, precious beryl. The most typical 

 colours are the light blue, greenish-blue, or bluish-green of aquamarine, the yellowish-green 

 of " aquamarine-chrysolite," and the yellow of yellow beryl, or golden beryl as the finest 

 specimens are called. Rose-red and colourless beryl is less common, and is not, as a rule 

 faceted. - These varieties differ from the emerald in colour ; they are also, as a rule, richer 

 in faces, as shown in Fig. 62, b to e, and in Plate XII., Figs. 4 and 5, the emerald, as already 

 noticed, seldom showing forms other than the simple combination of a hexagonal prism and 

 basal plane (Fig. 62 a). In the following pages aquamarine will be fully dealt with and 

 other varieties somewhat briefly, since they do not differ essentially from aquamarine in 

 character or mode and place of occurrence. 



Aquamarine is characterised by a pure sky-blue, bluish-green, or greenish-blue 

 colour-, very similar to the tint of sea-water ; hence its name, and the old saying that this 



