MINERALOGY; WITH A CLASSIFICATIOX OF SILICATES. 



49 



§ 58. We phu'o here also chrysotile, which constitutes the coramoii amianthus, and 

 has hitherto been regarded as a variety of serpentine, with which it agrees in centesimal 

 composition. It is, however, distinguished therefrom by much lower specific gravity, and 

 its fibrous character whit-h, like that of amiauthoid amphibole, indicates a prismatic crys- 

 tallization. As will be shown farther on, at least two other species, one phylloid and 

 another ophitoid, have been confounded under the name of serpentine. While the density 

 of these last is 260 or higher, that of chrysotile, according to three determinations, is 



II. 



Tribe I. Pectolitoid. 



214-2, 2-220 and 2-238, the first and the last being by E. S. Smith, and according to his 

 analyses corresponding to specimens containing respectively 2 23 and 336 of ferrous 

 oxyd.' If this oxyd be to the magnesia as 1 : 30, it would give for P a value of 15-51, 

 which, with a deu.sity of 2'22, would make V = 6-98. 



Fibrous silicates having the same centesimal composition as the last are, however, 

 met with, having a much higher specific gravity. A well defined mineral, described 

 many years since by the writer from Bolton (Quebec) under the name of picrolite, is 

 separable into long rigid elastic fibres, and has, with a specific gravity of 2-607, the com- 

 position, silica 43-70, magnesia 4068, ferrous oxyd 3-51, with traces of nickel and chro- 

 mium, and 12-45 of water, = 100-34. " 



§ 59. While the above species of unlike density agree in having the serpentine ratio, 

 3:4:2, there are several other hydrous silicates of magnesia which present other ratios, 

 and should like these be included among hydrospathoids. Such are the orthorhombic 

 sparry villarsite, with D = 2-98, which has been described as a hydrous chr3^solite, and is 

 represented by the atomic formula (nig,si,)oo-|- {aq, and the fibrous crystalline matricite 

 with D = 253, more hydrous in composition, with the Ibrmula (mgisii)o-, + laq, nearly. 



Amer. Jour. Science, 1885, xxix. 32. 



■' Geolojry of Canada, 186,3, ]>. 472. 

 Sec. III., 1885. 7. 



