SPINEL 297 



showing every possible gradation of colour, from deep red to white or colourless, are in 

 existence ; stones of the deepest tone of colour sometimes appear almost opaque. In contrast 

 to the ruby the colour of spinel is very uniform, and spots are rarely seen, so that far fewer 

 stones need to be thrown out from a parcel of spinels than would be the case with a similar 

 parcel of rubies. Faults of other descriptions are also less frequent in spinel than in ruby. 

 Like the ruby, the colour of the spinel remains unaltered by heat ; at very high temperatures, 

 however, the stone loses its colour, regaining it as it cools, but not passing through an 

 intermediate condition, in which the colour is green, as does the ruby. Experiments in this 

 direction made on valuable stones must be performed with care as the spinel is easily 

 cracked. 



The more deeply coloured a spinel is the more highly is it prized, provided, of course, 

 that the depth of its colour does not interfere with the transparency of the stone. The 

 colour of deep red stones is sometimes almost indistinguishable from that of the ruby. Such 

 stones are known as '■'■ruby-spinels'''' ("spinel-rubies'") (Plate I., Fig. 10), and are nob 

 infrequently sold as rubies. Carmine-red, blood-red, and poppy-red are the shades of 

 colour most admired in the " ruby-spinel." Very fine stones of cochineal-red or blood-red 

 rre known to jewellers as "gouttes de sang." 



Spinels of a rose-red or light shade of colour inclined to blue or violet are referred to as 

 " balas-rubies " (rubis balais) (Plate I., Fig. 9). They not infrequently combine with this 

 character a peculiarly milky sheen which considerably detracts from their value. Stones 

 the colour of which is more decidedly blue or violet resemble, although much paler, some 

 almandines, and are known as " almandine-spinels.'''' Violet spinels, which are not too pale 

 in colour, often resemble both the true amethyst and the " oriental amethyst," and indeed 

 have sometimes been put on the market under the latter name. There should, however, be 

 no danger of mistaking the one for the other, since the spinel is optically isotropic and is not 

 dichroic. To distinguish spinel fi'om almandine and other red garnets is more difficult, since 

 both agree in being optically isotropic and in the absence of dichroism. The colour of the 

 garnet, however, is usually much deeper than that of spinel, while, in the case of almandine, 

 the specific gravity (sp. gr. = 4), which is greater, and the hardness (H = 1\), which is less 

 than that of spinel, may be relied upon. Rose-coloured topaz may closely resemble" baias- 

 ruby," but then topaz is doubly refracting and strongly dichroic. Generally speaking, it 

 cannot be said that " ruby-spinel," " balas-ruby," and " almandine-spinel " are very sharply 

 marked oft' one from another, since stones showing intermediate characters are usually to be 

 found. 



The variety of spinel of a more or less pronounced yellow shade of colour is known as 

 rubicelle. This variety, which may be hyacinth-red, orange-yellow, or even straw-yellow, is 

 not esteemed very highly. The rubicelle which accompanies topaz and other precious 

 stones in Minas Novas, in Brazil, has received the name of " vinegar-spinel," on account of 

 its yellowish-red colour. At the particular locality at which it is found it is also known 

 as " hyacinth," also on account of its colour. The name " vermeille," though more 

 commonly applied to certain garnets, is also bestowed upon rubicelle of a decided 

 oranffe-red shade. 



Practically the same forms of cutting are used for the spinel as for the ruby. Finely 

 coloured, transparent stones are cut as brilliants, but the step-cut or a mixed-cut is 

 frequently employed, especially for darker stones. Foils of burnished gold or copper are 

 sometimes used for the purpose of improving the colour and lustre of cut stones. 



Spinels of good quality and up to 1 carat in weight are of ordinary occurrence ; 

 stones, the weight of which lies between 1 and 4 carats, are not infrequent, but large 



