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BERYL.
89

of fine stones in several places in the United States of America, in Brazil, and in British India. Beryl, or, rather, aquamarine, has been long worked in the District of Coimbatore in the Province of Madras.

Common beryls, but of muddy and even opaque hues, are sometimes found of enormous size. One from Grafton, New Hampshire, U.S., weighs 2900lb. It is 4ft. 3in. long, 32in. in one direction and 22in. in another, transverse to the last, across the crystal. A still larger crystal from the same locality was estimated to weigh nearly 21/2 tons. But some of the Russian aquamarines and transparent or precious beryls are of considerable size and without flaw. An aquamarine weighing 225 troy ounces, and without a flaw, belonged to the emperor of Brazil. Good specimens may be seen in the Mineralogical Gallery of the British Museum. Emeralds are rarely free from flaws, even in the case of small stones. So large and finely-coloured an emerald as No. 1284 in the Townshend collection is an exceptional stone; it is nearly 1/2 an inch across. The emerald is usually step, that is, trap cut; the table should not be large. Perfect stones of the best colour, and without flaws, sell for £40 to £60, occasionally even £140, per carat.

The emerald and the aquamarine consist essentially of a silicate of alumina and of the rare earth glucina. In the emerald Wohler has confirmed the presence of enough oxide of chromium to cause the green colour, for he coloured white glass with the same proportion, 0·19 per cent. Neglecting the oxide of iron, occurring in all varieties of beryl, and also the water and traces of other compounds, the composition in 100 parts of this mineral species will be:

Silica 66·8 Alumina 19·1
Glucina 14·1

The emerald was employed in antique Roman jewellery, sometimes in the form of slices of the native prisms, sometimes in beads, and very rarely for intaglios. Antique engraved gems of beryl or aquamarine are not quite so rare.