EMERALD, in natural history, a genus of precious stoner, of a green colour, and next in hardness to the ruby.
Our jewelers distinguish emeralds into two kinds, the oriental
oriental and occidental: the emeralds of the East-Indies are evidently finer than those of any other part of the world; but our jewellers, seldom meeting with these, call the American emeralds the oriental, and usually sell crystal accidentally tinged with green, under the name of the occidental emerald: these being also the most common, there has grown an opinion among the lapidaries, that the emerald is no harder than the crystal: because what they take to be emeralds, are in general only crystals.
The genuine emerald, in its most perfect state, is perhaps the most beautiful of all the gems; it is found of various sizes, but usually small; a great number of them are met with of about the sixteenth part of an inch in diameter, and they are found from this to the size of a walnut.
The emerald is of different figures like the diamond and many of the other gems, being sometimes found in a roundish or pebble-like form, but much more frequently in a columnar one, resembling common crystal: the pebble-emeralds are always the hardest and brightest, but are seldom found exceeding the size of a pea: the crystalliform ones grow several together, and are often larger: the pebble-kind are found loose in the earths of mountains, and sands of rivers; the columnar are found usually bedded in, or adhering to, a white, opaque, and coarse crystalline mass, and sometimes to the jasper, or the prasius.
The oriental emerald is of the hardness of the sapphire and ruby, and is second only to the diamond in lustre and brightness: the American is of the hardness of the garnet, and the European somewhat softer than that, yet considerably harder than crystal: It loses its colour in the fire, and becomes undistinguishable from the white sapphire.
The oriental emeralds are very scarce, and at present found only in the kingdom of Cambay; very few of them have of late been imported into Europe, inasmuch that it has been supposed there were no oriental emeralds; but within these ten years, some few have been brought from Cambay into Italy, that greatly excel the American ones. The American, being what our jewelers call oriental emeralds, are found principally about Peru; and the European are principally from Silesia.