Chemical Analysis of Precious Stones

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	412 THE CHEMICAL ANALYSIS OP PRECIOUS STONES. SAPPHIRE: RUBY: ORIENTAL TOPAZ. Pure alumina, coloured from admixture with oxide of iron.



	Sp. Gr. 3-99. Hardness only inferior to the diamond. Highly electric. Native form: six-sided prisms variously terminated, but more frequently found in rolled masses. SPINEL. Combination of alumina and magnesia, coloured red by a minute admixture of chromic acid, or blue by the protoxide of iron. τ>—ι τ»ι..„



	TOPAZ. Combination of alumina, silica, and fluoric acid.



	TURQUOIS. Considered by Fischer to be only clay coloured by oxide of copper ; but Jahn notices—

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