BERYL (EMERALD) 309 



subjection for an hour to a temperature at which copper readily melts. Although emerald 

 from this locality has been shown by Lewy to contain a small amount of organic matter, its 

 colour cannot, therefore, be due to this, but probably depends upon the presence of chromic 

 oxide, 0'186 per cent, of this substance having been found in the specimen examined by 

 Wfihler. That the deep green of the emerald can be produced by so small an amount of 

 chromic oxide has been proved by fusing white glass with the same percentage of this metallic 

 oxide, a glass having the intense green of the finest emeralds being produced. More recently 

 it has been shown that the colouring-matter of Uralian and Egyptian emeralds also is very 

 probably due to chromic oxide. 



Emeralds of good, full colour are distinctly dichroic ; the images shown by the 

 dichroscopc are respectively emerald- or yellowish-green and bluish-green. 



The colour of the emerald is not always distributed uniformly through its substance. 

 The differently coloured portions may occur irregularly or in layers ; in the latter case the 

 layers are, as a rule, parallel to the basal plane of the crystal, that is to say, perpendicular 

 to the prism faces. 



The transparency of the emerald is perfect only in rare cases. The majority of crystals 

 are rendered cloudy and dull, not only by fissures and cracks, but also by the presence of 

 microscopic enclosures, which in places are accumulated in large num bers. These enclosures 

 may be fluid or solid, scales of mica being specially common. Cloudy and opaque crystals 

 of emerald are usually dull in colour, approaching the characters of common beryl and being 

 useless for cutting as gems. Perfectly clear and transparent stones are naturally the most 

 valuable, but fissured and cloudy specimens, provided they possess the fine emerald-green 

 colour, have a certain value. 



Compared with other precious stones, the rarity of perfect specimens of emerald is 

 unique. The most common faults are those which have been just mentioned, fissures being 

 almost invariably present. Stones which are clouded by fissures are described as " mossv." 

 Irregularities in the distribution of colour, and dull and cloudy patches, are also frequently 

 to be seen. 



The disparity between the value of a perfect and of an imperfect emerald is enormous. 

 A faultless emerald is worth as much, or nearly as much, as a ruby, and certainly more than 

 a diamond. A one-carat stone, perfect in colour and transparency, is worth at least £S0, and 

 large stones, on account of their rarity, have a value out of all proportion to their size. As 

 a matter of fact, a perfect emerald weighing but a few carats is so rare that almost any price 

 will be given for it by collectors. Fissured stones, which are cloudy but of good colour, are 

 much cheaper ; when the colour is pale they are worth no more than £^ or even £^ 10s. 

 per carat. The value of such stones is more or less proportional to their size, large stones of 

 this description being by no means uncommon. 



Flawless emeralds of large size are extremely rare, so that only small stones are 

 available for cutting as gems. Emeralds of considerable size have been known, but their 

 quality leaves much to be desired ; moreover, in the case of large stones found and described 

 in early times, it must be remembered that the name emerald was applied to other stones of 

 a green colour. The ancient Peruvians are said to have numbered among their deities an 

 emerald the size of an ostrich's egg. Again, there is reported to be in the treasury at Vienna 

 an emerald which weighs 2£05 carats, while Schrauf states that in the same place is preserved 

 an ink-well cut out of a single stone, besides other large emeralds cut as table-stones. One 

 of the largest and finest emeralds known belongs to the Duke of Devonshire. It is a natural 

 crystal of the form characteristic of emerald, namely, a hexagonal prism with a basal plane. 

 This stone (Fig. 63) measures S inches across the basal plane, and weighs 8-^\ ounces or 



