486 



MINERALOGY 



H. = 5-5.5 ; G. = 2.22-2.29 ; Color, white with various tints, espe- 

 cially reddish ; Streak, white ; Luster, vitreous to nearly opaque ; 

 n = 1.487. 



B.B. Fuses easily to a colorless glass, gelatinizes with HC1. 

 Yields water in the closed tube. 



General description. Crystals simple tetragonal trisoctahe- 

 drons; rarely is it in combination with the cube or the rhombic 



dodecahedron. Like leucite, 

 these individual crystals 

 may be complexes, and the 

 outward form is only pseudo- 

 isometric, also massive. 



Analcite is formed in many 

 instances as pseudomorphs 

 after leucite, by an inter- 

 change of alkalies and hy- 

 dration; it is also formed 

 from sodalite and nepheline. 

 Analcite is one of the more 

 common zeolites and occurs 

 in rocks containing sodalite, 

 nepheline, or leucite, as a 

 secondary mineral, as well 

 as in the cracks and cavities 

 of the traps, diorites, and 



basalts. It is found at Bergen Hill and Princeton, New Jersey ; 

 in the Lake Superior region; Golden, Colorado; various points 

 in Nova Scotia ; and in Europe, in the Fassathal, Tyrol ; Aussig, 

 Bohemia ; Andreasberg, Harz ; Faroe Islands and Iceland. 



NATROLITE 



Natrolite. Na 2 (AlO)Al(SK) 3 ) 3 . 2 H 2 ; Orthorhombic ; Type, 

 Didigonal Equatorial ; a : b : c = .9785 : 1 : .3536 ; 100 A 1 10 = 

 44 23'; 001 A 101 = 19 52'; 001.011 = 19 28'; 110 A 111 =63 

 11'; Common forms, m(110), o(lll), b(010), c(001); Cleavage, 

 prismatic perfect, b imperfect ; Brittle ; Fracture, uneven ; H. = 

 5-5.5; G. = 2.20-2.25; Color, white, gray, yellow, or reddish; 

 Streak, white ; Luster, vitreous ; Transparent to translucent ; 

 a = 1.475; |5 = 1.478; y = 1.488; y - a = .013; Optically ( + ) 

 Axial plane = 010 ; Bx a = c ; 2 V = 61 56'. 



FIG. 505. Tetragonal-trisoctahedron of 

 Analcite, from Fassathal, Tyrol. 



