SILICATES, UTANATKS, KT< '. 



1S1 



General description. Crystals are prismatic or tabular, paral- 

 lel to the base; less often arc they pyramidal. Usually combina- 

 tions of the base, the unit pyramid of the first order, and tin unit 

 prism of the second. 

 The prism face is 

 vertically striated, 

 and the baseisoften 

 dull. 



Apophyllite is a 

 common mineral in 

 the fissures of the 

 traps of the New 

 England and Mid- 

 dle states. Beauti- 

 ful specimens of 

 stout prismatic 

 habit have been 

 taken from the va- 

 rious railroad cuts 



through Bergen FIG. 501. Apophyllite with Small Crystals of Albite. 

 Hill, New Jersey, Paterson, New Jersey. 



where it is asso- 

 ciated with other zeolites, prehnite, pectolite, and datolite. It is 

 also common in the Lake Superior copper region ; at Peter's 

 Point, Nova Scotia. Light pink crystals occur at Andreasberg in 

 the Harz, which are pyramidal in habit ; also at Aussig in Bo- 

 hemia, which is a noted European locality for zeolites in general. 



HEULANDITE 



Heulandite. H 4 CaAl 2 (SiOj) 6 . 3H 2 O ; Monoclinic ; Type, Di- 

 gonal Equatorial ; a : b : c = .4035 ; 1 : .4293 ; p = 88 34' = 

 001.100; 100, 110 = 21 58'; 001,011 =23 13'; 201,001=63 

 40' ; 001 A 201 = 66 ; Twinning plane, 100 ; Common forms, 

 c(001), b(010), m(110), t(201), s (201) ; Cleavage, b perfect ; 

 Brittle; Fracture, subconchoidal ; H. = 3.5-4; G. = 2. 18-2.22; 

 Color, white, gray, brown, or brick-rod; Streak, white; Luster, 

 vitreous, on cleavage face pearly; Transparent to translucent; 

 a = 1.498; p = 1.499; Y = 1 - 505 ; -y-a = .007; Optically 

 ( + ) ; Axial plane perpendicular to 010 ; Bx t normal to the ortho- 

 axis ; 2 V = to 90. 

 2i 



