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 [.86G]. Essentially a silicate of Al (34), 
K (9), and S'e (6), sometimes with Fe, H, and Mn, but very variable. 
45. BiOTiTE, Magnesia- w Uniaxal Mica [1.0]. Very variable, but essen- 
tially a silicate of Mg (19), itl (17), K. (9), Fe (8), and generally some 
H and Fe. 
46. LiPiDOLiTE, Lithia-mica fl.O]. Essentially a silicate of Al (2G), 
K (9), lii (4) with, hydrofluoric acid (5), and generally Mn, and often 
Fe and S. 
47. Chlorite [1.33]. A silicate of Fe (22), II (20), Big. (18), with 
fi (10) ; sometimes Fe replacing Al ; and Mn in small 
quantities. 
48. RipiDOLiTE [1.5]. A silicate of Mg (34), Al (16), Fe (4),"Fe (4), with 
H (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 simplest kind. 
50. AvQiT-E, Pyroxene ; IHopside; MalacoUfe, SahUte; and others [.5]. This 
mineral may, chemically, be separated into two classes, that contain- 
ing "il (5), including Augite proper ; and the non-aluminous class, 
including the other varieties mentioned. Excepting this distinction, 
the mineral consists essentially of a sihcate of Ca (in nearly a constant 
quantity), and Mg and Fe in variable proportions, the former gene- 
rally preponderating. Aluminous Augite, the most common variety, 
has Ca (21), Mg (14), Fe (7), 'H (5). Biopside has Ca (24), Mg (18), 
Fe (2), and generally small quantities of Mn. MalacoUte has Ca (23), 
Mg. (15), Fe (7), and some Mn. The black iron variety, Heden- 
bergite, 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 
aluminous .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. HoENBLENDE, Amphibole ; Tremolite; Actinolite; Antophyllite ; and 
others [.444]. According to Gmehn, 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, 
T 2 
