is in pegmatitic rocks which have been formed by dynamo-metamorphism, and to this group belong most of the crystals showing dislocation and absorption, and many of the more opaque varieties.
Beryl is a metasilicate of aluminium and beryllium, the latter element being so called from its presence in Beryl. Emerald probably owes its beautiful colour to the presence of traces of chromium ; many specimens of Beryl contain a little iron and calcium as well but they do not seem to be in any way essential, so the formula may be expressed as
Many specimens also contain
1 per cent, to 2 per cent, of chemically combined water. Beryl resists the action of all acids except hydrofluoric acid, by which it is attacked.
The distribution of Beryl is very wide. Probably the locality which, as far as is known, is the oldest is one in Egypt, where Emerald is believed to have been mined 1650 b.c., if not earlier. The crystals occur in mica-schist at Jebel Sikait and Jebel Sahara ; they are of a good colour, but rather pale.
It is very doubtful if the Emerald really came from India in Pliny's time ; certainly there is no authentic record of it having been found there, though other shades of Beryl, as the pale blue Aquamarine, occur in pegmatite bands in gneiss in the Punjab and in other parts of India. Many of the crystals are of large size, but are not of very good quality, being extensively fractured.
Peru was for a long time believed to be the home of the Emerald ; the Spaniards undoubtedly brought large numbers of this gem from Peru in the sixteenth century ; and it is recorded in "Cérémonies Religieuses" that, before the time of
