TALG. CHLORITE. 
41 
It consists of extremely thin parallel plates, having 
a bright metalUc 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 crystalhzes 
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, w^hile 
mica may be malted by the blo wpipe 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 <xf 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 primitive 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 ckloros, green. 
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