90 



MINEEA.L GALLeKV. 



Carbonates. Witherite, the carbonate of barium (18a), is used in the 

 manufacture of plate-glass and in France in that of beet-sugar. 

 Strontianite (18b), the carbonate of strontium, is one of two 

 minerals from which strontium-nitrate is made for use in the 

 manufacture of fireworks, owing to the fine crimson colour 

 which the salt gives to the flame : the strontium minerals are 

 also employed in connection with sugar-refining. Cerussite (18b) 

 is the corresponding carbonate of lead, and when abundant is 

 a valuable ore of that metal. 



Calcite (18e), a carbonate of the metal calcium, is represented 

 by a fine suite of specimens, illustrating an almost endless 

 variety of crystaUine form. The clear variety from Iceland is 

 largely used in optical instruments for polarising light. 

 Ghalybite, or Spathic iron ore (20h), is the carbonate of 

 iron, and a valuable ore of that metal. The most important 

 English iron-ore. Clay Iron-stone, 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 ; and by reason 

 of the high polish which it takes and its beautiful markings, is 

 much used for ornamental work of various kinds. 



suicates. Passing to the Silicates, we come to Olivine (22f), one of the 



less hard and least valued of the precious stones ; when of a 

 yellow colour it is known as Chrysolite, while the pistachio- 

 green variety is the Peridot of jewellers. Hiddenite (23a), a 

 rare emerald-green variety of Spodumene, is from Stony Point, 

 North Carolina. 



Asbestos (24c), a variety of Hornblende (a black mineral 

 common in rocks of igneous origin) used in manufactures, is found 

 in long fibres, and in some of its varieties 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 the 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- 



