SALMON — ON ROCKS. 



239 



to be the same (5 : 3) in Finite as in Cordierite. Cordierite is (with 

 Olivine) one of the few minerals containing silicate of Magnesia liable 

 to decomposition. 



44. Mica, Potash- or Biaxal Mica [.866]. Essentially a silicate of JLl (34), 



K (9), and Fe (6), sometimes with Fe, fl, and Mn, but very variable. 



45. BiOTiTE, Magnesia- or Uniaxal Mica [1.0]. Very variable, but essen- 



tially a sihcate of Mg (19), 11 (17), K (9), Fe (8), and generally some 

 H and Fe. 



46. LiPiDOLiTE, Lithia-mica [1.0]. Essentially a silicate of itl (26), 



K (9), lii (4) with hydi'ofluoric acid (5), and generally Mn, and often 

 ^e and fl. 



47. Chlorite [1.33]. A silicate of l^e (22), Al (20), (18), with 



S (10) ; sometimes Fe replacing Al ; and Mn in small 

 quantities. 



48. RiPiDOLiTE [1. 5] . A sUicate of % (34), Al (16), t^e (4),'"Fe (4), with 



(13). 



49. WoLLASTONiTE [.5]. Essentially a silicate of Ca (47), with generally a 



very small quantity of Mg, and often Fe. Supposed by mineralogists 

 to be an Augite of the simi)lest kind. 



50. AnGiTii, Pyroxene ; Diopside; Malacolitc, Sahlite; and otliers [.5]. This 



mineral may, chemically, be separated into two classes, that contain- 

 ing 'Al (5), including Augite proper; and the non-aluminous class, 

 including the other varieties mentioned. Excepting tliis distinction, 

 the mineral consists essentially of a silicate of Ca (in nearly a constant 

 quantity), and Mg and in variable proportions, the former gene- 

 rally preponderating. Aluminous Augite, the most common variety, 

 has Ca (21), Mg (14), ^e (7), Al (5). Diopside has Ca (24), Mg (18), 

 Fe (2), and generally small quantities of Mn. Malacolite has Oa (23), 

 Mg. (15), Fe (7), and some Mn. The black iron variety, Heden- 

 hergite, has Ca (21),Fe, (24), Mg (2). Augite also occurs in a fibrous 

 state, and is then called Amianthus or Asbestos. The O.Q. of the 

 non-aluminous class is .5 ; and, according to Bischof, that of the 

 alummous .666. The Al in this mineral is considered to act as an 

 acid. Augite. is extremely liable to decomposition. We find by 

 pseudomorphs that it is convertible into Mica and many other 

 substances. 



51. Hornblende, Amphibole; Tremolite; Actinolite; Antophyllite; and 



others [.444]. According to Gmelin, O.Q. = .416. This mineral is 

 closely aUied to Augite, but (as seen by the O.Q.) has more Si, 

 and also more Mg, but less Ca. The varieties can be divided into alu- 

 minous and non-aluminous. The aluminous are common Hornblende, 



