154 MAGNESIA. 



ture of some varieties, and is derived from the Greek aktin, 

 a ray of the sun. It is often mispelt actynolite. 



Asbestos. In slender fibers easily separable, and some- 

 times like flax. Either green or white. Amianthus occurs 

 in narrow seams, with a rich satin luster : much so-called 

 is serpentine. Ligniform asbestus is compact and hard ; it 

 occurs of brownish alpid yellowish colors, and looks somewhat 

 like petrified wood. Mountain leather occurs in thin tough 

 sheets, looking and feeling a little like kid leather.^ It con- 

 sists of interlaced fibers of asbestus, and forms thin seams 

 between layers or in fissures of rocks. Mountain cork is 

 .similar, but is in thicker masses ; it has the elasticity of 

 cork, and is usually white or grayish-white. 



The preceding light colored varieties contain little or no 

 alumina or iron. Composition of glassy actinolite, silica 

 59*75, magnesia 21*1, lime 14*25, protoxyd of iron 3*9, pro- 

 toxyd of manganese 0*3, hydrofluoric acid 0*8, (Bonsdorf.) 



2. Dark Cojlored Varieties. 



Pargasite. This name is applied to dark green crystals, 

 short and stout, (resembling fig. 1,) with bright luster, of 

 which Pargas in Finland is a noted locality. Gr = 3*ll. 



Hornblende. The black and greenish-black crystals and 

 massive specimens.- Often in slender crystallizations like acti- 

 nolite ; also short and stout like figures 1 and 2, the latter more 

 especially. It contains a large per-centage of oxyd of iron, 

 and to this owes its dark color. It is a tough mineral, as is 

 implied in the name it bears. This character however is 

 best seen in the massive specimens. Pargasite and horn- 

 blende contain both alumina and iron. 



Composition of hornblende, silica 48*8, magnesia 13*6, 

 iime 10*2, alumina 7*5, protoxyd of iron 18*75, protoxyd of 

 manganese 1*15, hydrofluoric acid and water 0.9, (Bons- 

 dorf.) 



Composition of pargasite, silica 46*3, magnesia 19*0, lime 

 14*0, alumina 11*5, protoxyd of iron 3*5, protoxyd of man- 

 ganese 0*4, hydrofluoric acid and water 2*2. * , . 



Amphibole is a name often given to this species. H^nj^vL 



The varieties of hornblende fuse easily with some ebulli 

 r tion, the white varieties forming a colorless glass and the 

 green a globule more or less colored by iron. 



What is asbestus and amianthus ? mountain leather and mountain 

 cork ? What is the peculiarity m composition of the light colored va- 

 rieties of hornblende? what of the dark varieties? 



