si I. it \\Tl. s. TTTANATES, ETC, 421 



ENSTATITE 



Enstatite. Magnesium metasilirate, M^iO 3 ; MgO = 40, 

 Sit). =(>(); Orthorbombic ; Type, Didigonal K<|ii;tt<ri;il ; a:b: 

 d = 1.0307 : 1 : .588 ; 100 A 110 = 44 8' ; 001 A 101 = 30 29' ; 

 ool till = -J!) 43'; 110 A 110 = 88 16'. Crystal forms rare, 

 c ool ), a (100), b (010), m (110) ; Twinning rare, forming lamellae; 

 Cleavage, prismatic, easy; Brittle; Fracture, uneven; H. = 5.5; 

 3.1-3.3; Color, gray, yellowish, olive to brown; Streak, 

 'hite to gray ; Luster, vitreous to silky, metalloidal and bronze- 

 like; Transparent to opaque; a = 1.665; P = 1.669; "y = 

 t.i.TJ; Y-a=.009; Optically (+); Axial plane = 010; Bx a 

 = c ; 2 V = 70, varies with Fe present. 



B.B. Fuses with difficulty (1400). Insoluble in acids. 



HYPERSTHENE 



Hypersthene. (Mg. Fe) SiO 3 ; with FeO greater than 10 per 

 cent. Orthorhombic ; Type, Didigonal Equatorial ; S : b : c = 

 .9713 : 1 : .5704 ; 100 A 110_=44 10'; 001 A 101 = 30 25'; 

 001 A Oil = 29 42'; 110 A 110 = 88 20'; Crystals, rare; Cleav- 

 age, b perfect, m and a less so ; Brittle ; Fracture, uneven ; 

 H. = 5-6 ; G. = 3.4-3.5 ; Luster, pearly to metalloidal, bronze-like ; 

 Color, dark brown, greenish to black ; Translucent to opaque ; 

 a == 1.692; p = 1.702; -y = 1.705; -y - a = .013; Optically 

 (-); Axial plane = 010; Bx a = a; 2V = 50 varies with Fe. 



B.B. Fuses with difficulty to a black slag. On coal in R. F. 

 becomes magnetic. Partially decomposed with HC1. 



General description. These two minerals are rarely found 

 showing crystalline faces. Large crystals of enstatite, combina- 

 tions of m, a, and b, terminated by a series of brachydomes and the 

 pyramid (223), occur at Bamle, Norway. Usually they occur 

 lamellar, foliated or fibrous in structure, cleavable at an angle 

 near 88. The transition form between enstatite and hypersthene 

 is known as bronzite from its peculiar metalloidal bronze-like 

 taster. 



In sections enstatite is either colorless or pale shades of yellow 

 or irreen. always much lighter than hypersthene, which is rather 

 reddish ; both are irregular or in rough crystalline outline, with 

 relief well marked, and surface appearing rough; cleavage well 



