284 



DESCRIPTIVE MINERALOGY. 



those from Bolton, by Mr. Nuttall. One of these locahties is four miles west of West-Point, 

 in the town of Cornwall ; another is four miles southeast of Woodbury furnace. In the town 

 of Monroe, it occurs two and a half miles southeast of Monroe works ; at the Two ponds ; 

 and in the Forest of Dean. At all these localities, it is found in the white limestone, and is 

 associated with spinelle, hornblende, etc. 



TALC. 



Talc, and Chlorite. Ckavdand. — Chlorite. Phillips. — Prismatic Talc Mica. Jameson. 



Glimmer. Mohs. 



Fig. 191. 



■ Prismatisehcr Talc- 



touch. 



Description. Colour green, sometimes passing into green- 

 ish black ; also greenish white, grey, and rarely blue. Streak 

 corresponding to the colour. It occurs regularly crystallized ; 

 also massive, disseminated, and in amygdaloid pieces. The 

 primary form is a right rhombic prism. Fig. 191. M on M' 

 120°. Cleavage parallel with P. Fracture slaty, scaly, foli- 

 ated, earthy and uneven. Lustre pearly on the terminal faces. 

 Yields to the nail, and when in powder is unctuous to the 

 Thin laminse are easily flexible, but not elastic. Ranges from translucent to opaque. 

 Hardness from 1 .0 to 1.5. Specific gravity from 2.70 to 2.80. Before the blowpipe, some 

 varieties lose their colour, and are difficultly fusible ; others are changed into a black scoria, 

 and do not fuse at all. 



Varieties. Chlorite. Under this name are included the dark green and generally opaque 

 varieties ; those which are regularly crystallized are called Foliated Chlorite ; the slaty, Chlo- 

 rite Slate ; the massive, scaly and foliated, Co7nmon Chlorite. 



Green Earth. This occurs in small masses, in, or lining the cavities of, amygdaloid. It is 

 dull and earthy ; yields to the nail, and is usually of dark green colour. 



Talc. This name is usually given to those specimens which are white, or very pale green. 

 Those which are most translucent, and have the highest degree of lustre, are called Common 

 Talc ; while those which are grey and green, with a slaty fracture and inferior lustre and 

 translucency, receive the name of Talc-slate or Indurated Talc. 



Composition. Foliated Talc — Silica 62.00, magnesia 87.00, oxide of iron 3.50, alumina 

 1 .50, water 6.00 {Vauquelin). 



Chlorite Slate — Silica 29.50, magnesia 21 .40, oxide of iron 23.40, alumina 15.60, water 

 7.40, lime 1 .50 (Grwner). 



Green Earth — Silica 52.00, magnesia 6.00, oxide of iron 23.00, alumina 7.00, water 

 4.00, potash 7.50 (Vauquelin). 



Geological Situation. Talc usually occurs in primitive mountains, sometimes forming 

 whole beds. It is often associated with the different varieties of serpentine, to which indeed 



