Besides its use for ornamental purposes, quartz finds a place as the material for lenses intended for delicate photographic work, because its transparency to the ultra-violet light is so much greater than that of glass. Spectacle lenses made of it are in demand, because they are not liable to scratches, and retain, therefore, their polish indefinitely. When fused in the oxyhydrogen flame, quartz becomes a silica glass, of specific gravity 2·2 and hardness 5 on Mohs’s scale, which has proved of great service for laboratory ware, because it withstands sudden and unequal heating without any danger of fracture; it has also in fine threads been invaluable for delicate torsion work, because it acquires not the smallest amount of permanent twist, in this respect being superior to the finest silk threads. Clear rock-crystal fetches little more than the cost of the cutting; citrine and amethyst are worth from 1s. to 5s. a carat, depending upon the quality and size of the stone; smoky-quartz is practically valueless; rose-quartz realizes less than 1s. a carat; and the value of cat’s-eye is also small—only 1s. to 2s. 6d. a carat. Tiger’s-eye at one time commanded as much as 25s. a carat, but the supply exceeded the demand, with the consequent collapse in the price. Beautiful, brilliant, and limpid rock-crystal is found in various parts of the world: in the Swiss Alps, at Bourg d’Oisans in the Dauphiné Alps, France, in the famous Carrara marble, in the Marmaros Comitat of Hungary, and in the United States, Brazil, Madagascar, and Japan. Small lustrous stones, known in their localities as ‘Isle of Wight,’ ‘Cornish,’ or ‘Bristol diamonds,’ are found in our own country. Brazil supplies stones out of which have been cut the clear balls used in crystal-gazing. The finest amethysts come from Brazil—especially the State of Rio Grande do Sul—and from Uruguay, India, and the gem-gravels of Ceylon; good stones also occur at Ekaterinburg, in the Ural Mountains. A splendid Brazilian amethyst, weighing 334 carats, and two Russian stones—one hexagonal in contour, weighing 88 carats, and the other, a deep purple in colour with a circular table, weighing 73 carats—are exhibited in the British Museum (Natural History). Cairngorm is known from the place of that name in Banffshire, Scotland, whence fine specimens have emanated; it is a gem much valued in that country. Fine cairngorm has also originated from Pike’s Peak, Colorado. Splendid yellow stones have had their birth in the States of Minas Geraes, São Paulo, and Goyãz, of Brazil—especially in the last. The fine Spanish smoky-quartz, which, as already stated, turns yellow on heating, comes from Hinojosa, in the Province of Cordova. The delicate rose-quartz is known at Bodenmais in Bavaria, Paris in Maine, United States, and Ekaterinburg in the Ural Mountains. The finest cat’s-eyes are found in India and Ceylon, and are high in favour with the natives. Greenish