114 MINERALS AND GEOLOGY 



77. Muscovite or Potash Mica : Silvery-white, grey, brown, green, 

 black, with pseudo-metallic pearly lustre. Rhombic in crystallization r 

 the crystals usually six-sided tables or prisms with strongly-pro- 

 nounced basal cleavage, but distinct crystals are comparatively rare. 

 Most commonly in foliated or scaly masses, tough and flexible. 

 H = 1.5 2.0 or cleavage surface, somewhat higher on edges of 

 folia. Sp. gr. 2.7 3.1. BB, whitens, and melts on the thin edges. 

 In the bulb-tube, usually gives off a small amount of water. Not 

 attacked by acids. Average composition : silica 46, alumina 30,. 

 sesquioxide iron 4, potash 10, water (and traces of fluorine) 2 to 4. 

 In some bright green varieties, 3 or 4 per cent, of oxide of chromium 

 is present. 



Muscovite is an essential component of ordinary granite, gneiss, 

 mica slate, and other crystalline rocks. It occurs, thus, more or less- 

 abundantly throughout the Laurentian area of Canada (Part Y), and 

 also amongst the metamorphic series of the Eastern Townships.. 

 Most commonly it forms small scaly masses, but, as stated by Sir 

 William Logan, large crystals and plates occur in a vein of graphic- 

 granite (see Part III) on Allumette Lake, north of Pembroke in 

 Renfrew County, and with black tourmaline on Yeo's Island, in the- 

 Upper St. Maurice. Large crystals of mica (apparently Muscovite) 

 are also said by Dr. Bigsby to occur in granite at Cape Tourmente 

 below Quebec. A green chromiferous variety in the form of small 

 scales in magnesite and dolomite has been recognized by Dr. S Gerry 

 Hunt in the Eastern Townships of Sutton and Bolton. 



78. Phlogopite (Magnesia Mica) : Yellowish-brown, brownish- 

 red, olive-green, yellowish-green, blueish-grey, <fec.,with pearly-metallic- 

 lustre. Rhombic : but occurring mostly in six-sided plates and 

 broad foliated masses, or in scaly particles, tough and elastic. Cleav- 

 age strongly pronounced in one direction. H = 2.0-2.5; sp. gr. 

 2.72 2.85. BB, whitens, and generally melts at the point and 

 edges. In the bulb-tube, most varieties yield traces of moisture. 

 Attacked, in powder, by hot sulphuric acid, the silica separating in 

 fine scales. Average composition: silica 41, alumina 13 to 18, 

 magnesia (with some oxide of iron (<fec.) 30, potash (with soda) 8 ta 

 10, water and fluorine 1 to 4. 



This species occurs most generally in association with the crystal- 

 line limestones and pyroxenic beds of the Laurentian series, and it is- 



