MICA AND THE MICA MINES. 663 



times used in windows, as they were in the seventeenth cent- 

 ury in Philadelphia, when glass was a luxury in the colonies. 

 The sheets are also used in the peep-holes of smelting furnaces, in 

 lanterns, in shades, and in the port-holes on board naval vessels, 

 where the vibrations would soon demolish less elastic glass. Mica 

 is an excellent non-conductor, and of recent years has been cut to 

 some extent into narrow strips for use in the construction of 

 dynamos. 



The scrap mica was formerly thrown away, with the excep- 

 tion of a small quantity used as a lubricating material, but it has 

 recently found a market in several new directions. Old waste 

 heaps are being bought up, for a few dollars a ton, and their con- 

 tents cleaned by being passed through a rough mill. This is sim- 

 ply a rotating cylinder of coarse wire screen with its axis slightly 

 inclined to the horizontal. The scrap is fed into the upper end 

 of the cylinder, and slowly discharges itself from the lower end. 

 As it makes its way from end to end, the sand and trash are sup- 

 posed to fall through the meshes of the screen. The cleaned scrap 

 is then shipped to Richmond, where it is ground into a coarse 

 powder and distributed to the various industries requiring it. 

 Large quantities are used in the manufacture of wall-paper. The 

 mica produces a sparkling surface which is thought to be decor- 

 ative, but at best the effect is somewhat bizarre. Considerable 

 amounts are used to produce the snow effects on Christmas cards, 

 and in stage scenery and other tinsel ; while smaller packages, 

 under the name of diamond dust, are sold as powder for the hair. 

 Much of the ground mica is sent to France, and this, oddly 

 enough, when the East Indian sheet mica is pressing our own 

 pretty heavily in the home market. 



The Latin world used the mica dust to strew over the Circus 

 Maximus, while mediaeval Europe knew the golden and silver 

 scales as cat-gold and cat-silver. 



But to go back again for a moment from the glass-house to the 

 mines themselves, there is much of interest in the rare and beau- 

 tiful minerals associated with the mica. Some of the mines are 

 quite noted for these by-products and are as attractive to a lover of 

 color as to the mineralogist. The mica itself is often the carrier 

 of curious forms. Frequently a mineral makes its way between 

 the laminae of the mica, and is thus forced to grow horizontally 

 instead of normally in three directions. This gives us curious 

 dendritic or tree-like forms which come out finely on holding the 

 mica up to the light. The oxide of manganese is most prone to 

 get caught in this way, and gives delicate tracery of dark brown 

 or black. Sometimes it is a garnet which is thus entrapped, and 

 then we have a brilliant little hexagonal plate of ruby glass, very 

 beautiful and very gem-like. By carefully taking off the outer 



