BERYL (AQUAMARINE) 319 



stone when placed in the sea becomes invisible. Aquamarine of a deep shade of colour is 

 very rare ; it is found, in small amount and of a fine deep, sapphire-blue, at Royalston in 

 Massachusetts, U.S.A. A distinction is sometimes made between sky-blue beryl and beryl 

 of a greenish-blue or bluish-green colour, the former being considered as aquamarine proper, 

 (Plate XII., Fig. 7), and the latter refei-red to as Siberian aquamarine. All pale bluish and 

 greenish beryls are, as a rule, however, included in the term aquamarine. 



The colours shown by precious beryl, and especially by aquamarine, are fine and 

 brilliant, and their beauty is still more noticeable in artificial light. The colour in every 

 case is supposed to be due not to chromium, as in the emerald, but to iron, which is always 

 present to the extent of ^ to 2 per cent. Experiments have been made to test the stability 

 of the colour of common greenish and yellow beryl from granite in the neighbourhood of 

 Dublin. After an hour's exposure to a temperature of 357" the crystals were observed to 

 be still translucent, but to have lost all their colour. When the crystals were fused a 

 colourless, cloudy mass was obtained. 



The dichroisin of aquamarine of a sufficiently deep colour is appreciable ; of the two 

 images seen in the dichroscope, one is a pure but pale blue and the other very pale 

 yellowish-green, almost colourless. The dichroism of specimens of a still deeper colour can 

 be observed with the naked eye. 



Aquamarine, and indeed all precious beryl, is, as a rule, very uniformly coloured, 

 irregularities in the distribution or character of the colouring being rare. Flawless and 

 perfectly transparent stones are also very much less rare than are emeralds of the same 

 description ; fissures and turbid or cloudy patches are sometimes to be seen, however. 

 These latter are caused by the enclosure of numerous microscopically small cavities closely 

 aggregated and either empty or containing a liquid. When these cloudy patches ai'e 

 present it is impossible to produce a good polish, although beryl, free from such faults, is 

 susceptible of a very brilliant polish. In some crystals transparent and cloudy portions 

 alternate, in which case the latter must be removed by cutting before the former can be 

 utilised. 



Precious beryl, including aquamarine, is, as a rule, cut in the brilliant form or in some 

 modification of the step-cut (Plate XII., Figs. 6 and 7). On account of the paleness of its 

 colour the cut stone must have a certain depth or it will show too faint a colour. The 

 lustre and colour of beryls is often improved by the use of foils ; thus aquamarine is placed 

 upon a silver foil or is mounted in a closed setting with a black lining. Very beautiful 

 stones with not too pale a colour are mounted in an open setting (a jour). A magnificent 

 faceted aquamarine, weighing 179J grams (875| carats), is to be seen in the mineral collection 

 of the British Museum. 



Crystals of beryl often have the form of long and relatively thin prisms, and in 

 correlation ^^•ith this the girdle of the faceted stone has often an elongated outline. Large 

 prisms of beryl are often cut in the East into dagger-handles and other articles of 

 considei-able size. In gems of such an elongated form the direction of greatest length 

 coincides with the direction of the principal axis of the crystal, and the stone is set in such 

 a position that its dichroism is most apparent. Aquamarine has been, and is, much used as 

 a vehicle for the expression of the engravers art ; its comparative softness renders the work 

 less arduous than is the case with many other precious stones. It is said that in ancient 

 times beryl was the material of which the lenses for spectacles were constructed, and that 

 from this originated the German word " Brille " (spectacles). 



Transparent, finely coloured and flawless crystals of precious beryl, specially of 

 aquamarine of considerable size, are by no means uncommon. Prisms of beryl of gem 



