The specific gravity is 2.67 to 2.73, making it one of the light minerals. Its lustre is vitreous and refraction double to a slight degree; its cleavage is imperfectly basal, and it becomes electric by rubbing. Acids do not attack the beryl, but it melts with borax and is soluble in salts of phosphorus. This stone is found in various colors, grass-green, pale-green, light-blue, greenish-blue, greenish-yellow, yellow, and sometimes pink. The most important of these colors is the grass-green, which forms a separate division of the beryl family, and is known as the emerald. EMERALD. The emerald or green beryl is one of the most highly prized of the gem stones. Its magnificent color has rightly been compared to the color of the fresh grass in spring, and in brilliancy this stone far exceeds all other green gems, excepting only the very rare green corundum or green sapphire. The emerald is said to be very soft when first withdrawn from the mine, but it hardens by exposure to the air. A perfect emerald of fair size is a rarity, so that the saying “an emerald without a flaw” has passed into a proverb. This stone is so light, compared to a diamond or sapphire, that a carat emerald will be very much larger than either of the above stones. The emerald is composed of: Silica 68.50 Alumina 15.75 Glucina 12.50 Peroxide of iron 1. Lime 0.25 Oxide of chrome 0.30 And traces of magnesia, of lime, and of soda. The vivid green color of the emerald is supposed to come from the oxide of chrome, as the other beryls do not contain chrome. Emeralds are found in New Granada, near Bogota, Egypt, East India, Burmah, Ural in Europe; Salzburg, Austria; Mt. Remarkable, South Australia; and North America. Some of the finest come from the mines of Muza, near Bogota, and the best stones are called Peruvian emeralds. During the conquest of Peru by the Spaniards, many very fine emeralds were destroyed by the invaders, who tested them by grinding and pounding, and concluded that the emeralds were worthless, because they were not as hard as the diamonds or sapphires. In 1587, Joseph D’Acosta returned to Spain with two cases of emeralds, each case weighing one hundred pounds. Green tourmaline sometimes passes for the emerald, but it is somewhat softer and considerably heavier. Olivines or chrysolites, if of a fine green color, sometimes resemble the emerald, but they are much heavier than the emerald and have a fatty lustre. Green spinels are heavier and harder than emeralds. BERYL. The second and less valuable division of the beryl family comprises the following colors: Clear light sky-blue, called by lapidaries aquamarine; very light greenish-blue, known as Siberian aquamarine; and a greenish-yellow variety, called aquamarine chrysolite.