tJoO SYSTEMATIC DESCRIPTION OF PRECIOUS STONES 



crystalline schists, such as gneisses and mica-schist ; it is found also in eclogite, serpentine, 

 and other rocks. As already stated, the crystals are either attached to the walls of drusy 

 cavities in the rock or embedded in it. Garnet is much less common in intrusive rocks, such 

 as granite, and all varieties, with the exception of black garnet, or melanite, are of sparing 

 occurrence in volcanic rocks. Garnets are also found in some limestones at places where the 

 rock has been baked by contact with a molten igneous rock, the garnets being a so-called 

 contact product in the limestone. The occurrence of precious garnet in its original situation 

 is, however, of little importance from the gem-seeker's point of view. But few garnets are 

 extracted from the solid rock ; for the most part they are picked up in the sands and gravels 

 of rivers and streams, having been set free by the weathering of the mother-rock and carried 

 away with the rest of the debris. 



We have already seen that there are many varieties of garnet differing from each other 

 in chemical composition. Garnets which agree in chemical composition are further classified 

 according to their external characters and are distinguished by particular names. Many of 

 these varieties are solely of mineralogical interest, but a few are suflRciently transparent to 

 be used for gems, and these we must now consider in some detail. They include the light 

 yellowish-red hessonite or cinnamon-stone, the dark violet-red almandine, the blood-red 

 pyrope from Bohemia, the magnificent " Cape ruby," the fine green demantoid from the 

 Urals, and, as rarities to the ordinary jeweller, the yellowish-red spessartite, the brownish- 

 green grossularite, and the black melanite. 



HESSONITE. 



Hessonite, or dnnamon-stone, as may be seen from the table of analyses above, is 

 essentially a calcium-aluminium garnet containing small quantities of ferrous and manganous 

 oxide, or, in other words, mixed with smlla amounts of iron-aluminium garnet and manganese- 

 aluminium garnet. The rich, warm yellowish-red colour of the stone is due to these two 

 constituents, calcium-aluminium garnet being of itself coloiuiess. The colour of this garnet 

 is hyacinth-red, sometimes inclined to orange or to honey -yellow. The colour varies somewhat 

 according to the distance at which the stone is held fi'om the eye. It appears distinctly red 

 only when held at some distance away ; close to the eye it often appears nearly pure yellow, 

 the red being almost completely invisible. Hessonite is also remarkable in that its colour 

 by lamp-light is considerably more brilliant and fiery than by day. The colour is well seen 

 in Figs. 7 and 8 of Plate XIV. ; the former is a representation of a druse of crystals having 

 the form of Fig. GQd, which is not unusual in hessonite ; and the latter of a faceted gem. 



The appearance of hessonite has been compared to sugar-candy, but more often to the 

 bark of the cinnamon-tree. It is from the latter resemblance that it has derived its name, 

 which is very appropriate, since most of the hessonite of gem-quality comes from the 

 cinnamon island of Ceylon. The colour of hessonite is, however, most strikingly similar to 

 that of hyacinth. So much alike are the two stones that they were only discovered to 

 belong to distinct species at the end of the eighteenth century. Previous to this, hessonite had 

 always been regarded as hyacinth (zircon), a mistake easily made, seeing that the stones are 

 found together in the same gem-gravels in Ceylon. Even now the stones are never distinguished 

 in the trade, and a large quantity of hessonite is sold as hyacinth. This is especially so in 

 the case of large specimens, for hyacinth scarcely ever occurs in crystals of largfe size, while 

 fragments of hessonite of good quality and considerable size are by no means rare. When 

 any difference is made by dealers in the application of the two terms, the darker specimens 

 of hessonite are referred to as hyacinth and the lighter as cinnamon-stone. The substitution 



