OF CENTRAL CANADA PART II. 91 



In Canada, this mineral has hitherto been noticed only in the 

 form of blueish and pale-red grains in the crystalline Laurentian 

 limestones of the Township of Burgess, Lanark County, Ontario. 

 At one locality (Lot 2, Con. 9), it is associated with quartz, ortho- 

 clase, pearly-white mica and sphene. 



42. Spinel : - Red, blueish, dark-green, black ; streak, white or 

 grey ; aspect, vitreous or stony. Regular in crystallization, and 

 commonly occurring in octahedrons, 

 either simple, or united in twin-forms 

 (Figs. 49 and 50). H = 8.0 ; sp. gr. 3.5 

 -4.5. BB, infusible* The red and 

 transparent varieties consist essentially 

 of alumina and magnesia : normally of Fm ' 49> FlG ' 50 ' 



alumina 72, magnesia 28, per cent. in the black varieties (Pleo- 

 naste, Ceylanite), the magnesia is largely replaced, however, by oxide 

 of iron ; and in the dark green or greenish-black varieties (Gahnite, 

 Automolite) it is almost entirely replaced by oxide of zinc. 



Small octahedrons and grains of a pale-blue colour (much resem- 

 bling the spinel which occurs under similar conditions at Aker, in 

 Sweden) are found in a crystalline limestone in the Seigniory of 

 Daillebout, Jolliette County, in the Province of Quebec. Large and 

 often very symetrical black crystals occur in crystalline limestone in 

 Burgess, Lanark Co. ; and less perfect examples of a similar colour, 

 accompanying fluor spar, apatite, and white orthoclase crystals, are 

 found in a vein of flesh-red calcite, in the Township of Ross, in 

 Renfrew County, on the Ottawa. 



H. SILICA AND SILICATES.* 



[This division comprises the different varieties of Quartz and Opal, 

 or silica in the free state ; together with the natural compounds of 

 silica with various bases, such as alumina, the iron oxides, magnesia, 

 lime, soda, potash, and the like. Some of these silicates yield water 

 when ignited ; others are anhydrous in their normal condition, but 

 frequently yield traces of water as the result of incipient decomposi- 

 tion. It is not possible t) arrange the silicates strictly in accordance 

 with their bases, without separating, in many instances, substances 

 which in general characters are closely allied ; and in some cases, an 



* For details respecting the crystallization characters of the silicates generally, the reader 

 may consult the Notes attached to the Mineral Tables in the author's Blowpipe Practice. 



