hedrons, while corundum ruby is hex'ago- 

 nal in crystallization. (See colored plate 

 in November number. ) Spinel is singly 

 refracting, in polarized light and corun- 

 dum doubly refracting. Spinel ruby is 

 infusible before the blowpipe, but on heat- 

 ing undergoes a curious series of changes 

 in color which are quite characteristic. 

 The red changes first to brown, and then 

 becomes black and opaque, but on cooling 

 the black changes to green, then becomes 

 nearly colorless and finally the stone re- 

 sumes its original red color. As a small 

 percentage of chromium is usually found 

 by analysis to exist in ruby Spinel, its 

 color is generally considered to be due to 

 this ingredient. While the Spinel ruby is 

 considered of less value than the corun- 

 dum ruby and is sometimes by fraud or 

 error substituted for the latter, it yet has 

 a definite value as a gem and is sold un- 

 der the name of Spinel ruby or some of 

 its varieties. This value is usually reck- 

 oned at about half that of the oorundum 

 ruby, although variations in quality of 

 the stones, as well as changes in demand, 

 cause differences of price. Thus Eman- 

 uel mentions a Spinel ruby oi good qual- 

 ity weighing 40 carats, which in 1856 was 

 sold for two thousand dollars, but which 

 in 1862 brought at public auction only 

 four hundred dollars. In 1866, however, 

 it was again sold for twelve hundred dol- 

 lars. The Spinel ruby of the French 

 crown jewels, weighing 56 carats, was 

 in 1791 valued at ten thousand dollars. 

 Not only is Spinel ruby related to cor- 

 undum ruby in color and use, but the 

 two are frequently associated together 

 in nature. The gem gravels of Ceylon, 

 Siam, Australia and Brazil contain both 

 kinds of rubies, and the ruby mines of 

 Upper Burmah, where the corundum 

 ruby occurs in a ci*ystalline limestone, 

 produce also large quantities of Spinel 

 rubies. Spinel rubies also come in large 

 quantity from Badakschan, in Afghanis- 

 tan, near the river Oxus, the name of 

 Balas rubies, by which they are often 

 known, being said to be derived from Be- 

 loochistan, or Balakschan. The Persians 

 have a tradition regarding these mines 



that they were disclosed by an earth- 

 quake which rent the mountain in twain. 

 The localities above mentioned furnish 

 nearly all the Spinel rubies of commerce. 

 A few have been found in North Amer- 

 ica at Hamburgh, New Jersey, and San 

 Luis Obispo, California. But these lo- 

 calities have never afforded any appre- 

 ciable supply. No Spinel rubies of great 

 size are known. Bauer mentions as the 

 largest known, two cut stones, one of 81 

 carats and the other 72^ carats, exhibited 

 at the London Exposition of 1862. The 

 King of Oude is said at one time to have 

 possessed a Spinel ruby the size of a pig- 

 eon's egg. 



Spinel occurs in many other colors be- 

 sides red, such as orange, green, blue and 

 indigo, as w^ell as white and black. Oc- 

 casionally colorless Spinels occur, and as 

 they cannot be distinguished by their be- 

 havior in polarized light from the dia- 

 mond, it is sometimes sought to substi- 

 tute them for the latter. They can be 

 detected at once, however, by their in- 

 ferior hardness. While Spinels of any 

 color, if transparent and free from flaws, 

 make desirable gems, the only colors 

 found in sufficient quantity outside of the 

 red to make an appreciable supply are 

 the blue and the black. The blue Spinels 

 resemble the sapphire in color, though 

 they are somewhat paler. They come 

 chiefly from Ceylon and Burmah, where 

 they occur together with the ruby Spinel. 

 The black Spinel is known as Ceylonite, 

 or pleonaste, and is also obtained chiefly 

 from Ceylon, although occurring of qual- 

 ity suitable for cutting at Mount Vesu- 

 vius in Italy. 



Like the ruby, Spinel can be made ar- 

 tificially, the process being to heat a 

 mixture of alumina and magrieisia with 

 boracic acid, and if the red color is de- 

 sired, a little chromium oxide. 



The Spinel ruby seems to have been 

 known to the ancients equally with the 

 corundum ruby, and the two were prob- 

 ably often confounded. The natives of 

 India call the Spinel the pomegranate 

 ruby and believe to this day that it pos- 

 sesses valuable medicinal properites. 

 Oliver Cummings Farrington. 



210 



