92 HOLLAND: MICA DEPOSITS OF INDIA. 



material raised in Bengal has a ruby-tint, a deep ruby-colour being the 

 common intensity of the light transmitted through " books " half an inch 

 thick. A greenish tinge more often characterizes the Nellore mica, but 

 other colours are also found— smoky brown, pale amber, bright olive- 

 green, and, more rarely, a bleached mica with silvery lustre. Formerly 

 only transparent mica, free of stains, found a sale'; but the objection to 

 the presence of the well-known brown and black, iron-oxide, inter- 

 laminar inclusions only holds for a limited portion of the uses to which 

 the mica is put, and such material now brings a good price as long as 

 it conforms to the desirable standard in toughness, cleavage, elasticity, 

 freedom from pressure-figure flaws and evenness of surface. 



With mica of the same quality, the price varies with the size of the 

 sheets, according to which the product is graded. The grades are 

 not, however, absolutely fixed, but the following list represents the 

 usual grading : — 



Specials, over 36 square inches. 

 No. I 2 1 to 36 „ 



No 2 15 „ 24 „ 



No. 3 10 „ 15 

 No. 4 6 „ 10 „ 



No. 5 3 „ 6 



The maximum rectangle obtainable from any sheet of irregular 

 shape is readily determined by placing it on a plate ruled into inch 

 squares, the squares being numbered along the direction of the two 

 co-ordinates from the left-hand lower corner. In addition to size, shape 

 has an influence on the market price ; amongst samples of mica of the 

 same superficial area, long strips are in greater demand than square 

 sheets,! whilst pieces cut to a specially required shape naturally bring 

 a special price, as they entail no waste. 



When Mr. Mallet visited the Behar mines in 1873, the native 

 miners recognised a series of grades, to which they gave the following 

 special names : — 



Karra, about 50 to 100 square inches. 



Rdsi, „ '30 „ 50 „ 



Manjhla, „ 20 „ 30 » 



Sanjhla „ 12 „ 20 „ 



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