Under the blow-pipe the opal loses its translucency and cracks but does not melt. Sulphuric acid will cause it to turn black, and in a cold solution of caustic potash the opal is almost entirely soluble. The precious or noble opal is found chiefly in the mines of Czernowitza, between Kaschau and Eperies, in Hungary, and in Gracias á Dios, a province in Honduras. In olden times, the Greek and Turkish merchants carried opals from Hungary to the Orient, and then they were shipped to Holland and sold in Europe as Oriental opals. The fire opal is of a yellowish-red color, and is found chiefly in Mexico, although it also occurs in Hungary, the Faroe Islands, Honduras, and Guatemala. The common opal is found in Ireland, Denmark, Frankfurt, Guatemala, and South Australia, and also in Hungary and Mexico. These opals are translucent without fire or reflection. The hydrophane is an opal that has lost color and brilliancy by reason of the evaporation of its water. If placed in water or alcohol, this stone becomes transparent, only to lose this quality when the water or alcohol has evaporated. The hydrophane becomes transparent more quickly in warm than in cold water, but most rapidly in alcohol. If boiled in oil, the hydrophane is said to retain its brilliancy for years. The cachelong is milky-white, and nearly opaque, and is found in small masses in the river Cach, in Bucharia, and also in Iceland. Although one of the most magnificent of the gem stones, the opal for many years was under the ban of superstition. Now, this splendid stone once more commands a foremost place in the jewelers’ art, and the opal mines of Hungary and Queensland are being worked to their fullest extent to supply the demand. PEARL. Although an organic product, the pearl is always ranked amongst the most precious of gems, and is distinguished by being the only gem that does not require the lapidary’s touch to bring out its beauties. Ancient writers have accounted for the origin of pearls by saying that they were formed of angels’ tears, or drops of dew from heaven, which, during the midsummer nights, fell into the gaping mouths of the pearl-oysters. According to modern scientific investigation, the formation of the pearl does not seem to be the result of healthy natural causes, but comes from the efforts of the oyster to rid itself of some foreign substance, like a grain of sand, a bit of shell or vegetation, or some unwelcome visitor in the shape of a small water insect. When annoyed by an intruding substance, the oyster begins to deposit its nacre, or mother-of-pearl, in regular concentric layers around the intruder, these layers gradually increasing in circumference and forming the pearl. Thus, like an onion, the pearl is merely a succession of layers or skins, starting from a small core, or nucleus, which is always present, though often only of microscopical size.