SILK 'ATMS, TITAN ATI 8, ETC, 



487 



B.B. Fuses at 2 to a colorless glass. Yields water in the 

 doM'.l tulic. Gelatinizes with HC1 ; the solution freed of silica and 



aluminium yields little or no precipitate with :imm<>nium carUmatc 

 (calcium). 



General description. Long prismatic in habit, the individual 

 crystals arc combinations of nearly a square prism terminated by 

 the unit pyramid, tetragonal in appearance; except for the occur- 

 rence of the brachypinacoid, as in case of the specimens from San- 



FIG. 506. Natrolite. Aussig, Bohemia. 



doen, Norway. Often in long acicular crystals joined in spherical 

 or divergent masses with the free end terminated ; in this habit, 

 it is very similar to pectolite, mesolite, and thomsonite. Also 

 granular but rarely massive, as that in which the neptunite and 

 benitoite is imbedded, occurring in San Benito County, California. 



Natrolite occurs filling amygdaloid cavities and cracks in basalt 

 and other related igneous rocks, as at Bergen Hill ; Moore's Sta- 

 tion, New Jersey ; at various points in Nova Scotia and Magnet 

 Cove, Arkansas. 



THOMSONITE 



Thomsonite. '(NaaCa^Al-^SiQj^ . 5H 2 O ; Orthorhombic ; Type, 

 Didigonal Equatorial ; a : b : c = .9932 : 1 : 1.0066 ; 100 , 110 = 44 

 48'; 001,101=44 37'; 001,011=45 11'; 001,111 = 55; 

 001,012 = 26 43'; Common forms, a (100), m(110), c(001), 

 d (401), p (111) ; Cleavage, b perfect, a less so ; Brittle ; Fracture, 

 uneven; H. =5-5.5; G. =2.5-3.4; Color, white, reddish to 

 lrown; Streak, white; Transparent to translucent; a = 1.497; 

 P = 1.503 ; -y = 1.52_5 ; <y - a = .028 ; Optically (+) ; Axial 

 plane = 001 ; Bx^ = b ; 2 V = 53 50'. 



