CARBONATES AND SILICATES. 
67 
The carbonate of barium, Witberite (18a), is used in the Carbonates, 
manufacture of plate-glass and in France in that of beet-sugar. 
Strontianite (18b), the carbonate of strontium, is the mineral 
from which most of the strontium nitrate is made for use in the 
manufacture of fire-works, owing to the fine crimson colour 
which it gives to the flame : it is also much employed in the 
process of sugar refining. Cerussite (18b) is the corresponding 
carbonate of lead, and when abundant is a valuable ore of that 
metal. 
Calcite (18e), carbonate of calcium, is represented by a 
fine suite of specimens, illustrating an almost endless variety 
of crystalline form. The clear mineral from Iceland is largely 
used in optical instruments for the polarisation of light. 
Chalybite, or Spathic iron ore (20h), is the carbonate of 
iron, and a valuable ore of the metal. The most important 
English iron ore, Clay iron-stone, is a mixture of chalybite and 
clay. Calamine (19h), carbonate of zinc, is an important zinc 
ore. Chessylite (2 Id) and Malachite (22b) are respectively the 
blue and green hydrated carbonates of copper, and are 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. 
Passing to the silicates we come to Olivine (22f), one of the Silicates, 
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 jewellery. Hiddenite (23a), a 
rare emerald-green variety of spodumene, from Stony Point, 
North Carolina. 
Asbestos (24c) is a variety of hornblende used in the arts ; 
it 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, unquenched or unquenchable, was applied 
to tlie mineral by the ancient Greeks, because, owing to its 
being unaltered by heat, wicks made of it were used in 
maintaining the perpetual sacred fires of their temples. 
Xapkins of asbestos were cleaned by being thrown into 
^lie fire ; asbestos cloth was also used in the process of cre- 
nation to keep the ashes of the body distinct from those of 
he fuel. It is now employed for more prosaic purposes, 
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