EMERALD. 



he had found 1-65 to 2-15 of water, and 0'3 

 to 0'35 carbonic acid, corresponding to some 

 organic matter present. 



BB alone, unchanged or becomes clouded : 

 at a high temperature, becomes rounded at 

 the edges, and ultimately a vesicular scoria 

 is formed. With borax forms a fine green 

 glass, which is colourless for Beryl. Slowly 

 dissolves with salt of phosphorus, leaving a 

 siliceous skeleton. 



Not acted on by acids. 



Emerald and Beryl are varieties of the same 

 mineral, under the former name being com- 

 prehended the rich green transparent speci- 

 mens, and those of other colours under the 

 latter. 



Until very lately, the colouring matter of 

 the Emerald was supposed to be due to the 

 presence of 1 or 2 per cent, of oxide of chro- 

 mium. This has, however, been proved to 

 be incorrect by M. Lewy's recent chemical 

 investigations into the formation and com- 

 position of the Emerald of Muzo. The quan- 

 tity of chromic oxide obtained by anah'sis 

 was so small as to be inappreciable, in fact, 

 too minute to be weighed separately, and 

 the beautiful tint of the Emerald is shown by 

 M. Lewy to be produced by an organic sub- 

 stance, Avhich he considers to be a cai'buret 

 of Hydrogen, similar to that called chloro- 

 phylle, which constitutes the colouring mat- 

 ter of the leaves of plants. 



Those Emeralds are of the darkest tint 

 which contain the greatest amount of organic 

 matter, and the colour is completely de- 

 stroyed at a low red heat, which renders 

 the stone white and opaque ; while, on the 

 other hand, heat produces no loss of colour 

 on those minerals which are coloured by 

 oxide of Chrome. (See Ouwarovite ) The 

 organic colouring matter of the Emerald is 

 probably derived from the decomposition 

 of the animals whose remains are now 

 found fossilized in the rock which forms 

 the matrix of the stone. This rock, which 

 is a black limestone, with white veins, con- 

 tains ammonites ; and specimens of Emerald 

 in fragments of the rock, shewing ammonites, 

 are exhibited in the mineralogical gallery 

 of the Jardin des Plantes, in Paris. 



Besides the organic colouring matter, M. 

 Lewy obtained from 1'65 to 2-15 of water; 

 from v/hich, in conjunction with the pre- 

 sence of fossil shells in the limestone in 

 which they occur, he has arrived at the 

 conclusion "that Emeralds have been formed 

 in the wet way, that is to sa}', that they have 

 been deposited from a chemical solution. 



According to the account of M. Lewy, Avho 

 personally visited the mine at Muzo, the 



EMERALD. 125 



Emeralds, when first extracted, are so soft 

 and fragile that tlie largest and finest speci- 

 mens can be reduced to powder merely by 

 rubbing them between the fingers, and the 

 crystals often crack and fall to pieces after 

 being removed from the mine, apparently 

 from the loss of water. 



When they are first found, it is necessary 

 to place them aside carefully for a few days, 

 until the water has evaporated from them. 

 M. Kuhlmann has endeavoured to prove 

 that the hardening of rocks and minerals is 

 not owing solely to the evaporation of 

 quarry-water, but that it depends upon the 

 tendency which all earthy matters possess 

 to undergo a spontaneous crystallization, by 

 slow desiccation, which commences from the 

 moment the rock is exposed to the air. 



The hardening of the Emerald by ex- 

 posure to the air does not appear to have 

 been known to the ancient inhabitants of 

 the portion of America more immediately 

 under consideration ; for their mode of test- 

 ing the value of a stone Avas hy striking it a 

 smart blow with a hammer, when it was 

 first taken from the mine. If it bore the 

 blow without injury, it was considered a 

 perfect stone, but if it broke, it was deemed 

 worthless. Under this rude mode of experi- 

 menting many valuable stones must neces- 

 sarily have been destroyed. 



As a precious stone, the Emerald ranks 

 next to tlie Ruby in value. It may be dis- 

 tinguished from all the other gems by its 

 colour, a pure green, without any admix- 

 ture of blue or yellow. 



It appears to the greatest advantage when 

 table-cut, and surrounded by brilliants, the 

 lustre of which contrasts agreeably with the 

 quiet tint of the Emerald. Imitations are 

 made Avith great success, both with respect 

 to colour and the flaws from which real 

 stones are seldom free. The last are pro- 

 duced by means of a sharp tool, after the 

 paste imitation has been polished. 



The Emerald is more valued in India than 

 in many other parts of the world, on account 

 of its foreign origin. 



In the East, advantage is taken of the 

 facility with which it may be broken at 

 right angles to its axis; and slices of prisms, 

 sometimes polished, but frequently with the 

 natural planes of cleavage preserved, are 

 mounted, surrounded Avith diamonds. This 

 was the usual mode of mounting them prior 

 to 1456. 



The Emerald was believed by the ancients 

 to be "excellent in its virtues." Amongst 

 other good qualities attributed to it, it was 

 supposed to be good for the eyes, on which. 



