THE NONMETALLIC MINERALS. 295 



smooth and flexible, as well as free from spots or inequalities of any 

 kind. It is stated that it should be sufficiently fissile to split into sheets 

 not above three one-hundredths inch in thickness, and which may be 

 bent without cracking into a circle of 3 inches diameter. Strips of 

 various dimensions are used in building up the armatures, the more 

 common sizes being about 1 inch wide by 6 or 8 inches long. Musco- 

 vite serves the purposes well, but is less used than phlogopite, the 

 latter serving equally well, and being less desirable for stoves and fur- 

 naces. Black mica would doubtless serve for electrical purposes, could 

 it be procured in sheets of sufficient size. 



Mica scraps such as until within a few years have been thrown away 

 as worthless are now utilized by grinding, the product being used for 

 a variety of purposes, noted below. The material is as a rule ground 

 to five sizes, such as will pass through sieves of 80, 100, 140, 160, and 200 

 meshes to the inch, respectively. The prices of this ground material 

 vary from 5 to 10 cents a pound according to sizes. Large quanti- 

 ties of this ground material are used in the manufacture of wall paper, 

 in producing the frost effects on Christmas cards, in stage scenery, and. 

 as a powder for the hair, being sold for the latter purposes under the 

 name of diamond powder. The so-called French "silver molding" is 

 said to be made from ground mica. It is also used as a lubricant, and 

 as a nonconductor for steam and water heating; in the manufacture of 

 door knobs and buttons. It is stated further that owing to its elas- 

 ticity it can be used as an absorbent for nitroglycerin. rendering ex- 

 plosion by percussion much less likely to occur. Small amounts of 

 inferior qualities are also mixed with fertilizers where it is claimed to 

 be efficacious in retaining moisture. A brilliant and unalterable mica 

 paint is said to be prepared by first lightly igniting the ground mica 

 and then boiling in hydrochloric acid, after which it is dried and mixed 

 with collodion, and applied with a brush. Owing to the unalterable 

 nature of the material under all ordinary conditions, and the fact that 

 it can be readily colored and still retain its brilliancy and transparency, 

 the ground mica is peculiarly fitted for many forms of decoration. 

 Much of the ground material now produced is stated to be sent to 

 France. 



The chief and indeed only use for lepidolite thus far developed is in 

 the manufacture of the metal lithium and lithia salts. 



Prices. The total value of the cut mica produced annually in the 

 United States during the past ten years has varied from $50,000 to over 

 $360,000, while the value of the imports has varied between $5,000 

 and $100,000. The price of the cut mica, it should be stated, varies 

 with the size of the sheets, the larger naturally bringing the higher 

 price. The average price of the cut mica, all sizes, is not far from 

 $1 a pound, while the scrap mica is worth perhaps half a cent a 

 pound. The dealers' lists, as published, include 193 sizes, varying 



