72 HOLLAND: MICA DEPOSITS OF INDIA. 



V.-USES OF MICA. 



A common question, and one which shows a justifiable curiosity, is- 

 occasioned by imperfect knowledge of the uses for which this peculiar 

 mineral is purchased. As far as possible, I have gathered notes of the 

 various ways in which mica is consumed in the Arts, but to an in- 

 genious mind there must be numberless other ways in which some or all 

 of its peculiar properties can be utilized. No other mineral, and no 

 artificial substance, combines the natural properties of mica : its highly 

 perfect cleavage, by which it can be split into the thinnest films ; its 

 transparency to light, combined with a comparative opacity to radiant 

 heat rays ; its imperfect powers of conducting electricity, giving it 

 great value as an insulator ; its chemical stability when exposed to the 

 weather, or to corrosive oils and acids ; the great flexibility of its folia,- 

 combined with a high elastic limit and consequent power to resist 

 violent shocks or sudden changes of temperature, give mica a range of 

 usefulness which is not likely to be imitated cheaply by any artificial 

 substance. 



The earliest use of the mineral was probably in the form of 

 window-panes, as well as for lanterns, and mica was in consequence 

 known as Muscovy glass ( Vitrium Muscoviticum), which suggested the 

 name muscovile, reserved in 1850 by the late Prof. J. D. Dana for the 

 special variety which is by far the most abundant form so used. It was,, 

 however, subsequently replaced by the cheaper artificial substance, 

 glass ; but in the early stages of glass manufacture, when the processes 

 for annealing plates had not been developed, mica was still retained for 

 use in places where the window-pane would be subject to sudden 

 shocks or violent vibrations, as, for example, on men-o'-war, where 

 the shocks of heavy-gun firing shattered the badly annealed glass. 

 Since, however, the processes for annealing glass have been developed 

 to such perfection, and since it has been made possible to cast curved 

 and variously shaped sheets of glass, it has entirely replaced mica for 

 such purposes. In ordinary lanterns, too, mica has been replaced by 

 ( 62 ) 



