240 
THE GEOLOGIST. 
Pargasite, and basaltic hornblende. General composition about 
Mg (15), Ca (12), 11 (10), J'e (7—10), very variable. Uralite is also an 
aluminous variety. The non-aluminous varieties are Tremolite and 
J dmoZiie (magnesia-lime hornblende) with 5lg (24), Ca (14), and J'e, 
amounting to (4) in ActinoUte ; and Antophyllite (magnesia-iron 
variety) with Mg (24), J'e (14), Mn (2). The fibrous variety. Asbestos 
t or Amianthus, has generally the composition of Tremolite or 
ActLnoIite. 
In this mineral the Al is supposed to act partly as an acid, re- 
placing the Si and forming aluminates, and partly as a base ; but the 
subject is very obsciu'e. It is less subject to decomposition than 
Augite, from its containing less Ca ; but yet it is hable to many 
series of alterations. 
62. Htpersthene [.5]. A silicate of Mg (12—2.5), Fe (25—12), Ca (3), and 
often Al and Mn. Marked by its small contents of Ca, and wide 
replacement by each other of Mg and Pe. 
53. Bronzite [.5]. A silicate of Mg (30) and Pe (9), with often some 
Mn and S, and sometimes Ca. 
54. Dtallage [..5]. A sOicate of Mg (17), Ca (16), f'e (7), II (3), 
with H (2). 
55. Serpentine [.76]. Many varieties. A silicate of Mg (40) and Pe 
(2-6), with H (12). 
56. Talc ; Steatite, SpecMein [.428 or .437]. Average composition of 
sihcate of Mg (32), Pe (2), with H (3). Steatite is the compact variety, 
but has always a ciystalhne structure. Meerschaimi is the amorphous 
variety, with four per cent, additional water. 
67. Olivine, Chrysolite, Peridot [1.0]. A silicate of Mg (45) and Pe (15), 
with very little Mn and Fe. In the gi-een transparent variety. 
Chrysolite, there is the highest proportion of Mg (50) and a com- 
parative decrease of f'e. 
