. Precious stones, a popular account of their characters, occurrence and applications, with an introduction to their determination, for mineralogists, lapidaries, jewellers, etc. With an appendix on pearls and coral. Precious stones; Pearls; Corals. 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
. Precious stones, a popular account of their characters, occurrence and applications, with an introduction to their determination, for mineralogists, lapidaries, jewellers, etc. With an appendix on pearls and coral. Precious stones; Pearls; Corals. 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.) •^ 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, assume
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