294 REPORT OF NATIONAL MUSEUM, 1899. 



where the mineral oeeurs in large foliated masses together with quartz 

 forming the gangue minerals of the tin veins. Also found in Moravia 

 (Specimen No. 62580, U.S.N.M.). 



Uses. Until within a few ytnirs almost the only commercial use of 



mica was in the doors or wnndows of stoves and furnaces, the peep- 

 holes of furnaces and similar situations where transparency and resist- 

 ance to heat were essential qualities. To a less extent it was used in 

 lanterns, and it is said, in the portholes of naval vessels, where the 

 vibrations would demolish the less elastic glass. In early days it was 

 used to some extent for window panes, and is, in isolated cases, still so 

 used to some extent. For all these purposes the white variety musco- 

 vite is most suited. For use in stoves and furnaces ''the mica is gen- 

 erally split into plates varying from about one-eighth to one sixty- 

 fourth of an inch in thickness. In preparing these plates for market 

 the first step is to cut them into suitable sizes. Women are frequently 

 employed in this work, and do it as well as, if not better, than the 

 men. The cutter sits on a special bench which is provided with a huge 

 pair of shears, one leg of which is firmly fixed to the bench itself, while 

 the movable leg is within convenient grasp. 



The patterns according to which the mica is cut are arranged in a 

 case near at hand. They are made of tin, wood, or pasteboard, accord- 

 ing to the preference of the establishment. Generally they are simple 

 rectangles, varying in size from about four square inches to eighty. 



The cutter selects the pattern which will cut to the best advantage, 

 lays it on the sheet of mica, and then, holding the two firmly together, 

 trims off the edges of the mica to make it correspond to the pattern. 



The cleaning process comes next. The cleaner sits directly in front 

 of a window and must examine each sheet of cut mica by holding it up 

 between her eyes and the light. If there be any imperfections, and 

 there nearly always are, they must be removed by stripping off* the 

 offending layers of mica until a clear sheet remains. 



Finally, the cut and cleaned mica is put up in pound packages and 

 is ready for the market. There is an enormous waste in the processes 

 of preparation. One hundred pounds of block mica will scarcely yield 

 more than about fifteen pounds of cut mica, and sometimes it is even 

 less. The proportion varies, of course, with different localities.^ 

 Professor Kerr states with reference to the North Carolina mines that 

 there is a waste of from nine-tenths to nineteen-twentieths of the 

 material, even in a good mine. 



Mica being a nonconductor is of value for insulating purposes, and 

 since the introduction of the present system of generating electricity 

 there has arisen a considerable demand for it in the construction of 

 dynamos and electric motors. For these purposes the mica must be 



1 Engineering and ^Mining Journal, LV, 1893, p. 4. 



