GUIDE TO THE MINERALOGIC COLLECTION'S 91 



The cleavable masses are pink or gray. Granular masses of 

 a white or reddish color are common. 

 Anorthite occurs in many volcanic rocks. 



31 eta silicates 



Leucite KAl(Si0 3 ) 2 



Leucite is a silicate of potassium and aluminium. It crystal- 

 lizes in trapezohedrons (fig. 207) and is often found in irregular 

 grains disseminated through lava and volcanic 

 rock. The luster is vitreous and the color light 



gray or white. 



Pyroxene group 



The following species though falling in the 

 orthorhombic, monoclinic and triclinic systems, 

 exhibit a marked similarity in crystal habit and 

 in the angle of the fundamental prism, which 

 varies but slightly from 87°. This relation is emphasized by the 

 fact that a more or less pronounced cleavage takes place parallel 

 to this fundamental prism in all species referred to this group. 



Enstatite (bronzite) (MgFe)Si0 3 



Enstatite is essentially a silicate of magnesium but often con- 

 tains some iron replacing the magnesium. The iron-bearing 

 variety is known as bronzite and grades into hypersthene with 

 increased percentage of iron. 



Enstatite rarely occurs in orthorhombic crystals of columnar 

 habit. It is usually found in lamellar or fibrous masses, brown, 

 gray or green in color and in the variety bronzite with a sub- 

 metallic or bronzelike luster. 



It is frequently found in basaltic and granular eruptive rocks 

 and -is quite common in stony meteorites. It occurs at Tilly 

 Poster, Putnam <•<>. mid at Edwards, St Lawrence <•<». X. Y. 



Hypersthene (MgFe)SiO 



Hypersthene is ;i silicate of magnesium and iron. With a 

 decreasing proportion of iron hypersl bene grades into enstatite. 

 Orthorhombir crystals are pare. Tin- mineral is usually found 

 in dark green to black foliated masses, frequently showing a 

 metalloidal luster somewhal similar x> thai of bronzite. Hypers- 



