360 SYSTEMATIC DESCRIPTION OF PRECIOUS STONES 



mode of occurrence is the same as in Arizona, and wliere it is collected by the Comanche 

 Indians. 



Of all vai-ieties of garnet one of the finest is the dark, blood-red pyrope, which occurs 

 in association with diamond in South Africa. This also was at first supposed to be ruby, 

 and was collected and sold as such for some time, hence the term " Cape ruby.'''' Several 

 different kinds of garnet are found in association with diamond at the Cape. Some are of 

 a deep wine-red colour, some of a hyacinth-red, almost the colour of hessonite, while others, 

 fewer in number, are brownish-yellow and deep blood-red. 



The last named is the much prized " Cape ruby " and is the only one cut as a gem. It 

 is a magnesium-aluminium garnet containing some manganese oxide and ferrous oxide, and 

 differing but slightly in chemical composition from the Bohemian pyrope, as ir.ay be seen 

 from the analysis quoted above. The " Cape ruby " must therefore be classed with pyrope 

 and not with almandine, as is sometimes incorrectly done. Not only on account of its 

 chemical composition, but also on account of its specific gravity, which is 3-86 (that of 

 Bohemian pyrope being 3'7 to 3'8, and that of almandine 4-1 to 4-3) and of its colour, 

 should this classification be adopted. The colour approaches indeed much more closely to 

 that of pyrope, being an almost pure carmine-red more or less tinged with yellow and not 

 very deep in shade (Plate XIV., Fig. 6), thus differing distinctly from the columbine-red of 

 a good almandine. The hardness is 1\, the same as that of Bohemian pyrope and of 

 almandine. The "Cape ruby" fetches larger prices than any other garnet, stones of 

 moderate size being worth £\0 to ^12 10s. per carat. 



It has already been stated that the " Cape ruby " occurs in association with diamond 

 in South Africa. It is found in the form of irregular angular grains with an uneven surface 

 in the diamond-bearing rock known as the " blue ground " and the "yellow-ground.'" The 

 mother-rock is thus an olivine-rock, or, more commonly, the weathered equivalent of this, 

 namely, serpentine, just as is the case with the pyrope of Bohemia, North America, and all 

 other localities. The " Cape ruby " is far less abundant than is the paler red pyrope by 

 which it is accompanied. The grains are larger on the whole than are the grains of pyrope 

 found in Bohemia and America ; they never exceed a certain maximum size, however, which 

 is much less than that of the largest diamonds found at the same place. The residue of 

 heavy minerals obtained by washing the diamantiferous material contains, besides diamonds, 

 red garnets and green grains of an augitic mineral ; and from this residue the diamonds and 

 " Cape rubies " are picked out. In the diamond-bearing rock of the " dry diggings " the 

 " Cape ruby " is somewhat of a rarity, being far more abundant, though still uncommon, in 

 the " river-diggings," that is to say, in the sands and gravels of the Vaal river, where it 

 sometimes occurs in pebbles so smooth and rounded that they appear to have been polished. 

 Here, as in the " dry-diggings," the stone is collected as a secondary product. 



There still remains to be described a new variety of red garnet, recently (1898) described 

 by Messrs. W. E. Hidden and J. H. Pratt, for which the name RHODOLITE is proposed. 

 In many respects it is intermediate between almandine and pyrope, but more closely related 

 to the latter, though differing from both in colom-. Its occurrence in association with ruby 

 at Cowee Creek and Mason's Branch in Macon County, North Carolina, has been mentioned 

 already in the description of corundum. It is found as water- worn pebbles in the gravels 

 of these streams, and also, together with ruby, in a decomposed, basic igneous rock, known 

 as " saprolite," and, in the form of small crystals, enclosed in crystals of ruby. The colour 

 is pale rose-red inclining to purple like that of certain roses and rhododendrons, hence the 

 name rhodolite. It lacks the depth and intensity of colour which makes garnets, as a rule, 

 such dark-looking stones especially by artificial light. The peculiarly beautiful rose tint of 



