102 



MINERALS AND GEOLOGY 



FIG. 64. 



present, and rarely exceeds 4 or 5 per cent. Crystallization, 

 tially clinorhonibic. Sp. gr 2.9 3.3. Scarcely, if at all, attacked 

 by acids.] 



52. Amphibole (including Tremolite, Actinolite, Hornblende, &c.): 

 Green of various shades, greenish-white or almost colourless, brown, 

 black. Clinorhonibic in crystallization, the crystals mostly oblique 

 rhombic or six-sided prisms, with the obtuse prism-angle (Y on Y 

 in the accompanying figures) = 124 30'; 

 but occurring commonly in acicular forms, and 

 in fibrous, lamellar and granular masses. 

 H == 5.5 6.0 ; sp. gr. 2.9 3.4 (mostly 

 3.03.2) BB, melts more or less easily, the 

 dark varieties yielding a magnetic bead. 

 Scarcely or not at all attacked by acids. The greenish-white and 

 colourless or pale-grey varieties of this mineral are usually known 

 as Tremolite ; the bright-green, or dark-green, acicular and fibrous 

 varieties, as ^ctinoliie ; and the green massive varieties, as well as 

 those in green, brown, or black, thick crystals, are commonly termed 

 Hornblende, a name applied by many authors to the species 

 generally. A. soft, siiky variety, in 'fibrous masses, belonging, how- 

 ever, partly to Pyroxene (No. 53), is also known as Asbestus or 

 Amianthus, but this variety does not appear to occur in Canada, our 

 so-called asbestus being a fibrous serpentine, containing about 12 

 or 14 per cent, of water. (See under No. 83, below.) Average 

 composition : silica (40 60 per cent.) magnesia (15 25 per 

 cent.), lime (12 15 per cent.), with, in most varieties, a small 

 amount of protoxide of iron, &c. Alumina, when present, varies in 

 amount from less than one to above 15 or 16 per cent, but the 

 latter is only found in a few dark-coloured hornblendes of excep- 

 tional occurrence. 



Amphibole is an essential constituent of many eruptive and 

 metamorphic rocks, such as syenite, diorite or greenstone proper, 

 syenitic gneiss, hornblende slate, &c. ; and it is present accidentally 

 in many crystalline limestones and other rocks. It occurs in various 

 localities throughout the large area occupied by the Laurentian 

 series of Canadian strata (see Part Y), and also in the more modern 

 metamorphic district of the Eastern Townships. Examples 

 of Tremolite occur more especially in the crystalline (Laurentian) 



