SII.K 'ATI'S, TIT \\.\TKS, ETC. H.l 



The name andalu>ite i> derived from the noted locality of Anda- 

 lusia, in Spain. 



Andalusite in weathering is decomposed ly percolating waters 

 containing alkalies, forming mir.-i^ and kaolinite. 



SILLIMANITE 



Sillimanite. Al(A10)SiO 4 ; A1O 8 =_63; SiO 2 = 37; Ortho- 

 rhoml.ic; A : b : c = .970 : 1 : ? 110 A 110 = 88 15'; 230 A 230 

 = 69; Common forms, a (110), b (010), m(110), h (230) ; 

 Cleavage, b perfect; Brittle; Fracture, uneven; .H. = 6-7; 

 G. = 3.23-3.24; Color, shades of gray, brown, and green ; Streak, 

 white; Luster, vitreous; Transparent to opaque; a = 1.660; 

 p = 1.661; -y = 1.681; -y - a = .020; Axial plane = 010; 

 Bx a = c; Optically (+) ; 2V = 31 19'. 



B.B. Like andalusite. 



General description. Crystals are slender, elongated, parallel 

 to the vert ieal axis ; from this habit the mineral is sometimes known 

 as fibrolite. Terminations have never been observed. Also in 

 compactly massed fibers arranged parallel or radiating. In sections 

 sillimanite may be distinguished from andalusite by the fibrous 

 structure, by the higher double refraction yielding interference 

 colors of the second order, and by the optical character being posi- 

 tive. 



In occurrence and decomposition by weathering, it resembles 

 andalusite. 



CYANITE 



Cyanite. Disthene, Al(AlO)SiO 4 ; _A1 2 O 3 = 63, SiO 2 = 37 ; 

 Tridinic ; Type, Centro-symmetric ; & : b : c = 0.8994 : 1 : .7089 ; 

 a = 90 5' ; (3 = 101 2' ; y '= l ^ 44' J 100 A 010 = 73 56' ; 

 100 A 001 = 78 30'; 010 A 001 = 86 45'; 100 A 110 = 34 17'; 

 Common forms, a (100), b (010), c (001), m(110); Twinning 

 plane, 100 ; Cleavage, a perfect, b less so and parting parallel to c ; 

 Brittle; Fracture, fibrous; H. = 5-7.25; G. = 3.56-3.67; Color, 

 blue, white, reddish, and green; Luster, vitreous; Transparent 

 to translucent; a = 1.717; p = 1.722; y = 1.729; y - a = 

 .012 ; Optically ( - ) ; Bx a nearly normal to 100 ; 2 V = 82. 



B.B. Like andalusite. 



General description. Crystals are long, bladelike in habit, 

 combinations of the two pinacoids a and b, with the unit prism ; 



