Calcite (18e), a carbonate of the metal Calcium, is represented by a fine suite of specimens, illustrating an almost endless variety of crystalline form. The clear variety from Iceland is largely used in optical instruments for polarising light. Chalybite, or Spathic Iron-ore (20h), is the carbonate of Iron, and a valuable ore of that metal. The most important English Iron-ore, Clay Ironstone, is a mixture of Chalybite and Clay. Calamine (19h), a carbonate of Zinc, is an important Zinc-ore. Chessylite (21d) and Malachite (22b) are respectively the blue and green carbonates of Copper, and are used as ores of that metal. Malachite is found in large masses; by reason of the high polish which it takes and its beautiful markings, it is much used for ornamental work of various kinds. [Sidenote: Silicates.] Passing to the Silicates, we come to Olivine (22f), one of the less hard of the precious stones; when of a yellow colour it is known as Chrysolite, while the green variety is the Peridot of jewellers. Hiddenite (23a) is a rare emerald-green variety of Spodumene, and Kunzite is a lilac-coloured variety which is used as a gem stone. Asbestos (24c), a kind of Hornblende (a mineral common in rocks of igneous origin), is found in long fibres; in some of its varieties it is so flexible that it can be woven into gloves and other articles. The term Asbestos, meaning unquenched or unquenchable, was applied by the ancient Greeks, because, owing to being unaltered by heat, wicks made of this mineral were used in maintaining the perpetual sacred fires of their temples. Napkins of Asbestos were cleaned by being thrown into the fire; Asbestos-cloth was also used in the process of cremation to keep the ashes of the body distinct from those of the fuel. It is now employed for lining iron-safes, packing for steam-pipes and boilers, and in gas-stoves, for which purposes its low conductivity for heat renders it serviceable. Jade or Nephrite (24d), a valued mineral, belongs to the same group as Hornblende. The various shades of colour and the beautiful polish which this tough mineral will take are illustrated by specimens in the case. Several worked specimens from New Zealand and China are exhibited. An immense water-worn mass, weighing 1156 lb., found some years ago in Asiatic Russia, is mounted on a separate stand near by. Meerschaum (23g), the light soft porous mineral used for tobacco-pipes, is a hydrated silicate of Magnesium. Serpentine (25a) is another hydrated Magnesium-silicate: the ease with which it is worked and polished, its green colour, and varied markings render it much sought after as a material for mantel-pieces, tables, and other indoor work: exposed to the weather it soon loses its polish.