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The Sapphire is not so easy to imitate, as its hardness exceeds that of the ruby, and imitations containing its known constituents, or of glass, are invariably softer than the natural stone. As before remarked, almost any form of corundum other than red is, broadly, called sapphire, but giving them their strictly correct designations, [...] This mineral is a species of crystal, or crystalline alumina -an almost pure anhydrous alumina, Al2O3 -in many varieties, both of shape and colour. The chief stone is the ruby, considered, when large, to be of even more importance and value than the diamond. There are many other red stones in this group; sapphires, [...] |
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