Emerald (Sp. esmeralda; Gr. from to shine, whence the old name of smaragd and the German Smaragd), a. name given to the finest crystals of the mineral species beryl, transparent and of rich green colors derived from oxide of chrome, which is present in the proportion of about 1 per cent., but, according to Vauquelin, sometimes as much as 3.5 per cent. (See Bekyl.) They are found in metamorphic rocks, the granites, and mica schists. The finest specimens come from near Muzo, N. N. W. of Bogota, South America. Here it occurs in isolated crystals or in nests in a clay slate, a rock containing cretaceous fossils in its limestone concretions, and not in veins, as has been stated. A perfect hexagonal crystal from this place, 2 in. long and measuring across its three diameters 2 1/4, 2 1/5, and 1 7/8 in., and weighing 8 oz. 18 dwts., is in the cabinet of the duke of Devonshire. A still finer specimen, but only 6 oz. in weight, is in the possession of Mr. Hope, and cost £500. Emeralds of much larger size, but of less beauty, are found in Siberia, on the river Tokovoya, in mica schist. One in the royal collection is 14 1/2 in. long by 12 broad, and weighs 16f lbs. troy.
The true emeralds of the ancients are said to have been principally obtained from Mt. Zabarah in Upper Egypt, where the old workings were discovered by the French traveller M. Cailliaud, and reopened by Mehemet Ali. They are, however, inferior to the South American gems. The Peruvian emeralds were famous from the time of the conquest of that country by Pizarro. They were obtained in the barren district of Atacama, and worked by the native artists with the skill of the modern lapidary. To this day a river and a village of Ecuador are known by the name of Esmeral-das, from the abundance of emeralds formerly found in that region. Mexico at the same early period had produced crystals of rare beauty, which were no less appreciated and highly valued by the rulers of the Aztecs than were those of Peru by its incas. For one of the fine emeralds brought by Cortes on his return to Europe some Genoese merchants are said to have offered him 40,000 ducats. They had been cut by the exquisite workmanship of the Aztecs, one in the form of a rose, the second in the form of a horn, the third like a fish with eyes of gold, and the fourth like a little bell, with a fine pearl for the tongue; the fifth, which was the most valuable, was a small cup with a foot of gold, and with four little chains of the same metal attached to a large pearl as a button.
From these sources were probably-obtained the magnificent emeralds now in the royal collection at Madrid, some of which are stated to be as large as those of the duke of Devonshire, and of the finest water. The emerald has long been highly esteemed, ranking in value next to the diamond and the ruby. Pliny states that in his time those of considerable size, which were free from defects, were sold at enormous prices. - The color of the emerald is of a finer green than that of any other stone, having different shades, some of verdigris or grass green, and some of a paler hue. They all appear best by daylight, and to retain their effect by candle light they require to be set with small diamonds or pearls. Emeralds are generally cut in the form of a square table, with bevelled edges, the lower surface being cut into facets, parallel to their sides. Beudant, in his Mineralogie, gives the value of emeralds of fine colors, and free from flaws, as follows: one of 4 grains, 100 to 120 francs; of 8 grains, 240 francs; of 15 grains, as high as 1,500 francs; and he cites a fine stone of 24 grains which was sold at 2,400 francs. - Immense emeralds are mentioned by ancient authors, but they were undoubtedly glass imitations.
Such was the colossal statue of Serapis in the Egyptian labyrinth, 13 1/2 ft. high; also an obelisk in the temple of Jupiter, 60 ft. high and 6 ft. broad, composed of four pieces. Sir J. Gardner Wilkinson remarks that the forming of these huge blocks of glass was a greater triumph of art than imitating the stones. Egypt was the country especially noted for the manufacture of artificial emeralds, and Pliny says that they succeeded so completely that it was " difficult to distinguish false from real stones." - The oriental is not, like the true emerald, a silicate of alumina and glucina, but is a green, transparent variety of corundum, and therefore nearly pure alumina, differing from the sapphire only in color. It is the rarest of gems, and from this and its superior hardness, although inferior in color, it is highly prized. Mr. Emanuel of London says that he has only met with one specimen; but in the autumn of 1872 Dr. J. Lawrence Smith had sent to him from the territory of Montana a quantity of rolled pebbles, which were found to be corundum. They were flattened hexagonal prisms with worn edges, and were either colorless or green, varying in shade from light to dark; none were red.
They are found on the Missouri river, near its source, about 160 m. above Benton, and are obtained from bars on the river, where considerable gold is also found. The corundum is scattered through the gravel, which is about 5 ft. in depth, lying upon the bed rock. It is most abundant on the Eldorado bar, 16 m. from Helena. One man could collect on this bar from one to two pounds per day. Dr. Smith has had some of the stones cut, one of them very perfect, of 3 1/2 carats, of a fine green, almost equal to the best oriental emerald.