280 SYSTEMATIC DESCRIPTION OF PRECIOUS STONES 



being only occasionally met with. It is hoped that a more systematic working of these 

 deposits, especially at Ruby Bar, will result in more frequent discoveries of stones of good 

 colour. In America, as in Australia, garnets have been frequently mistaken for the more 

 costly ruby, and have been collected and sold as such. 



In Europe red corundum, suitable for cutting as gems, is pi-actically absent, and the 

 same is the case in the continent of Africa, the so-called " Cape rubies,'" occurring in South 

 Africa in association with diamond, being not ruby but garnet. 



AuTiFiciAL Production. — Ruby is the only valuable precious stone which hitherto has 

 been produced by artificial means in crystals of fair size showing all the characters of the 



natural minerals. The honour of this achievement belongs to 



the French chemist Fremy, whose efforts in this direction have, 



after many trials, a,t last been crowned with success. His object 



was attained by fusing together in an earthen crucible at a high 



temperature (1500° C), a mixture of perfectly pure alumina ( AlgOg), 



potassium carbonate, barium (or calcium) fluoride, and a small 



amount of potassium chromate, the whole mass being kept in a 



molten state for a week. The series of reactions which take place 



Fig. 58. Crystal of under these conditions probably begins with the formation of 



artificially prepared ruby aluminium fluoride. This compound, as a result of contact with 



Magnified. (After Fremy.) •j.nxii.i.j^ i*. 



the moisture oi the atmosphere and lurnace gases — a contact 



rendered possible by the porous nature of the crucible — yields aluminium oxide (alumina). 

 This, by taking up chromic oxide from the potassium chromate, assumes a red colour and 

 crystallises out as ruby. When isolated, after cooling, from the fused mass, in which 

 the crystals are embedded, they are found to differ in nowise from naturally occurring 

 crystals of ruby. 



The artificial crystals so formed have always the form shown in Fig. 58, which 

 represents a rhombohedron in combination with extensively developed basal planes, faces 

 which bound natural crystals of ruby also, as shown in Fig. 53, a — d. The thin tabular 

 crystals produced b)'^ this method are always of small size, never exceeding J carat in 

 weight. Their size is increased when larger amounts of material ai"e allowed to interact in 

 the crucible. The colour of the artificial product varies from pale to dark red, according 

 to the conditions of the experiment. The most beautiful and characteristic ruby-red 

 colour was produced by the addition of 3 to 4 per cent, of potassium chromate. The 

 colour-results seem, however, somewhat difficult to control, for the crystals often more or 

 less incline to a violet colour, sometimes, indeed, being quite blue, while crystals' coloured 

 red at one end and blue at the other have been occasionally produced. From these 

 observations Fremy concludes that the colour of naturally occurring sapphires, as well 

 as of rubies, may be due to chromium. More than 3 to 4 per cent, of the chromium 

 salt is taken up only with difficulty, and the crystals receive a violet tint, differing 

 very markedly from the colour of naturally occurring rubies. 



Artificially formed rubies which, of course, differ in no way from naturally occurring 

 stones, except in their mode of formation, have been mounted as gems, both in a cut and in 

 an uncut condition. Having the same hardness as natural corundum, they have also been 

 utilised as the pivot-supports of watches. 



The cost of production of artificially made rubies is so high that they are no 

 cheaper than stones formed by nature; moreover, their small size strictly limits 

 their general application. Before his death Fremy expressed a hope that crystals of 

 much greater size would result from experiments conducted in a crucible of 50 litres 



