Considering the particular emerald which is a variety of beryl -although the name emerald in the trade is applied somewhat loosely to any stone which is of the same colour, or approaching the colour of the beryl variety -this emerald only differs chemically from the beryl, just described, in possessing an addition of oxide of [...]
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The beryl is a compound of silicates of beryllia and alumina, with the formula 3BeOSiO2 + Al2O3,3SiO2, or 3BeO,Al2O3,6SiO2. It differs very little indeed from the emerald, with the exception of its colour. In the ordinary varieties this is somewhat poor, being mostly blue, or a dirty or a greenish yellow; the better kinds, [...] The name topaz is derived from the Greek topazos, which is the name of a small island situated in the Gulf of Arabia, from whence the Romans obtained a mineral which they called topazos and topazion, which mineral to-day is termed chrysolite. The mineral topaz is found in Cornwall and in the British Isles [...] There are certain stones and other minerals which, owing to their possession of numerous microscopically fine cavities, of a globular or tubular shape, have the appearance of “rays” or “stars,” and these are called “asteriated.” Several of such stones have been discussed already in the last chapter, and in addition to these star-like rays, [...] 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, [...] |
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