Beryl (Gr. ), a mineral composed of silica 66.8, alumina 19.1, glucina 14.1 = 100. The union of the emerald and beryl in one species, which Pliny says was suggested in his time, was first recognized on crystallographic grounds by De Lisle, and more satisfactorily through measurements of angles by Hauy, and chemically by Vauquelin. The beryl, emerald or smaragd, and aquamarine are all the same mineral species, and only distinguished from each other by their blue and yellow shades of green, or by the delicacy of the crystals. The beryl is sometimes also white. The emerald is more transparent and of finer colors than the beryl, and makes a handsomer gem. Aquamarine is a beautiful sea-green variety. The brilliant green color of the emerald is due to the presence of a minute quantity of oxide of chromium; beryl and aquamarine derive their colors from the oxide of iron. The beryl crystallizes in regular 6-sided prisms, which are often striated with longitudinal channels. Its hardness, rated at 7.5 to 8 on the mineralogical scale, is less than that of topaz and greater than that of quartz.
Its specific gravity is 2.7. The crystals are found in metamorphic limestones, in slate, mica schist, gneiss, and granite rocks, generally as single crystals or in clusters, rather than in veins. There are many celebrated localities of gigantic beryls and beautiful emeralds in various parts of the world. Upper Egypt produced the mineral in ancient times, and it is still found in the mica slate of Mount Zabarah. Siberia, Hindo-stan, Limousin in France, Peru, and Colombia . have all furnished splendid emeralds. The largest beryls known have been found in Ac-worth and Grafton, New Hampshire, and in Royalston, Massachusetts. One from Grafton measures 4 ft. 3 in. in length, 32 in. through in one direction and 22 in another transverse, and weighs 2,900 lbs. Another is estimated to weigh nearly 2 1/2, tons, measuring 45 in. through in one direction and 24 in. in another. A crystal in the museum at Stockholm, found in Sweden, is considered to be the largest in Europe; it weighs 80 lbs. The value of the specimens is not at all dependent on their size. The large crystals are of coarse texture and feeble lustre, and possess no beauty.
As the beryl expands by heat in a direction perpendicular to the principal axis, and contracts on the line of the axis, there is a point where the expansion and contraction exactly neutralize each other, and a section across this would maintain a constant length. Soleil recommends the cutting of prisms in conformity with this direction, to be used as normal units of measurement.