ALUMINA. 



849 



Fig. 340. 



Fig. 341. 



Fig. 342. 



Rockland County. At Pier- 

 mont, apophyllite occurs in the 

 greenstone, but it has not hitherto 

 been obtained in well defined crys- 

 tals. Figs. 340, 341 and 342 repre- 

 sent the forms which have been 

 observed in the same formation at 

 Bergen hill, New-Jersey. M on 

 M 90° ; P on M 90° ; P on s 120° 

 5' ; M on s 128° 20' ; s on « 104° 

 18'. 



PREHNITE. 



(In honour of its discoverer, Gol. Prehn.) 



Prehnite. HiHtj, Cleaveland, Phillips, Thomson, Shepard and Beudant. — Azotomoos Prehnite. JameiBn. — 



Aiotomer Triphan-Spath. Mohs. 



Description. 



Fig. 343. 



Colour commonly green of various shades, but sometimes grey and white; 

 It occurs regularly crystallized ; also in scopiform, stellular and fibrous 

 concretions, and massive. The primary form is a right rhombic 

 prism. Fig. 343. M on M' 100° {Phillips), 102° 30' {Beudant). 

 y; I II Cleavage distinct parallel to P ; less so, parallel to M. Fracture un- 



even. Lustre vitreous, except on the face P, which is pearly. Ranges 

 from transparent to translucent. Hardness from 6 . to 7 . 0. Specific 

 gravity from 2.90 to 2.95. When heated, it becomes electric. By 

 calcination, it yields water. Before the blowpipe, it melts into a white, greenish or pale 

 yellowish frothy glass ; with borax, it forms a transparent bead. Slowly soluble in muriatic 

 acid, from wliich solution an abundant precipitate is produced by oxalate of ammonia. 



Prehnite has a lower degree of lustre than stilbite or heulandite, which it sometimes re- 

 sembles. It does not, like many of the zeolite family, form a jelly with acids. By calcina- 

 tion, it yields less water than chabazite or epistilbite. 



Composition. Silica 43.60, alumina 23.00, lime 22.33, oxide of iron 2.00, water 6.40 

 ( Tliomson). 



Geological Situation. This mineral usually occurs in primitive rocks, or in trap and 

 greenstone. It is found in both these situations in this State. 



LOCALITIES. . 



Essex County. Prehnite occurs massive and semi-crystallized, and of a yellowish white 



