432 NATURAL HISTORY. 



vitreous ; transparent to translucent. Occurs in Bohemia 

 and Nova Scotia. 



IV. Mica Family. Mica is distinguished by its 

 peculiar vitreous structure, and luster which passes from 

 transparent to the translucence exhibited by mother-of- 

 pearl. Elastic and of different hues, from colorless to 

 red, and verging from yellow to bronze and black. H. 

 = 2 to 2.5 ; G-. = 2.86, to 3.1. Many varieties. 



The Common Mica is sometimes of crystallized struc- 

 ture, but mostly occurs in laminate crystal plates ; com- 

 mon everywhere, and is the principal constituent of 

 granite, gneiss, and mica slate. The colorless mica, on 

 account of the toughness, transparency, and the thinness 

 of its folia, is known in Siberia as Marienglass, and 

 divided into thin plates, like panes, is used in place of 

 glass in windows. The laminae of the Siberian mica often 

 exceeds a yard in diameter. The fine fragments of mica, 

 mixed with sand, used in Germany for numerous pur- 

 poses, such as giving a lustrous sparkle to various orna- 

 mental works, etc., and according to color is known as 

 gold or silver sand. This brilliant metallic sparkle so 

 well resembles that of gold or silver, that those who are 

 not acquainted with it are easily deceived. Hence it is 

 called cat-gold, or cat-silver. 



Talc is of inferior hardness. = 2.6 to 2.8 ; elastic ; 

 formed in laminoe, but also occurs compact or tabular. 

 Recognized by its unctuous feel, and mother-of-pearl-like 

 structure. Color always light gray, pale yellow, or 

 greenish- white, translucent. Usually found in compact, 

 pearly, foliated masses, forming large structures of rock. 

 The purest and handsomest specimens are brought from 

 the Alps ; those of Graubunden are most esteemed. The 

 white variety of talc is employed in the manufacture of 



