TALC. CHLORITE. 



41 



It consists of extremely thin parallel plates, having 

 a bright metaUic lustre; its colour is yellow, gray, 

 blackish green, white, and brown. The plates are 

 very elastic, which distinguishes it from talc, which 

 in some respects resembles it. As the plates are 

 transparent like glass, it is often used for doors in 

 lanterns, and for windows in ships, where a more 

 brittle material, like glass, would be liable to be 

 broken; as it will bear heat without injury, it is also 

 used in stoves. Mica is soft, and may be easily 

 scratched with a knife. It sometimes crystallizes 

 in six-sided prisms. It forms an essential ingre- 

 dient in granite, gneiss, and mica slate, and is 

 accordingly abundant in every primitive country. 

 In Siberia it is quarried, and employed for the same 

 purposes as glass. Plates of it three feet square 

 have been brought from that country. 



Talc bears some resemblance to mica, but is unc- 

 tuous to the touch, and not elastic, though flexible. 

 It is also softer than mica, and is infusible, while 

 mica may be melted by the blowpipe into an enam- 

 el. It is either of a greenish or a silvery white col- 

 our, and has a shining, pearly lustre. It is found 

 in primitive rocks, such as granite and serpentine, 

 but is not an abundant mineral. 



Chlorite,'^ — This mineral closely resembles talc, 

 is of a darkish, dull green colour, has a glistening 

 lustre, and is soft and rather soapy to the feel. It 

 seems to be composed of a compact mass of minute " 

 scales. In its chemical composition, it contains 

 less silex, but more magnesia than talc. Chlorite 

 slate is one variety of this mineral; and this is 

 found in beds in prin* ive mountains, and some- 

 times contains crystals of mica, garnets, magnetic 

 iron, &c. 



Hornblende is of a dark green or black colour, 

 heavier, but less hard than quartz or feldspar; it 



♦ From chlorost green. 

 D 



