OF CENTRAL CANADA PART II. 97 



Also in granitic veins, with tourmaline, on the North River, in St. 

 Jerdme, Terrebonne County ; and, according to the Reports of the 

 Geological Survey, in a syenitic rock, composed of red feldspar and 

 black hornblende, on Pie Island, Lake Superior. Transparent 

 varieties of this mineral are employed in jewellery, under the name 

 of Jargon or Hyacinth. 



45. Chiastolite : Grey or pale-red. Occurs in rectangular and 

 rhombic prisms, mostly of narrow diameter, and in compound 

 groupings, which present the appearance of a simple prism with 

 dark cross on the transverse section (Fig. 



56), the cross consisting of slate or other 

 rock matter, in which the prisms are im- 

 bedded. Found also in granular masses. 

 H = 5.5 7.7 ; sp. gr. 3.1 3.2. BB, FlG . 56 . 



quite infusible. The powder by ignition with nitrate of cobalt 

 (p. 34) assumes a fine blue colour. General composition : silica, 37, 

 alumina 03. Occurs in somewhat indistinct crystals imbedded in 

 argillo-micaceous slates, in the immediate vicinity of intrusive masses 

 of granite, on Lake St. Francis, in Megantic County. 



46. Tourmaline : Of various colours green, blue, black, brown, 

 yellow, red, and sometimes colourless ; but Canadian varieties are 

 either black, brown or brownish-yellow. The black variety is com- 

 monly known as Schorl, and is quite opaque. Hexagonal (or rather 

 Hemi-Hexagonal) in crystallization, the crystals being almost in- 

 variably three-sided prisms (or these, with bevelled edges, produc- 

 ing a prism of nine sides). The cross fracture is thus as a rule more 

 or less distinctly triangular. The prisms are often longitudinally 

 striated, and are frequently 



much broken, especially when 

 imbedded in quartz (Fig. 58). 

 Tourmaline occurs also very 

 generally in columnar, acicu- 



lar and fibrous masses. H= FI Q . 57. FIG. 58. 



6.57.0; sp. gr. 3.03.3. BB, the black and most of the brown 

 varieties melt very easily, the other varieties being for the greater 

 part quite infusible. Nearly all exhibit electrical properties when 

 heated. Composition somewhat variable, but the essential compo- 

 nents consist of : silica (averaging about 38 per cent.), boracic acid 

 8 



