ALUMINA. 



349 



Fig. 310. 



Fig. 341. 



Rockland County. At Pier- 

 mont, apophyllitc occurs in the 

 greenstone, bnt it has not liitlierto 

 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 1 20° 

 5' ; M on s 128° 20' ; s on s 104° 

 18'. 



M 



II 



PREHNITE. 



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



Prebnitc. //.sy, Ckavehnd^ Phillips, Thomson, Shepard and Beudant. — Axotomous Prchnitc, Jameson. — 



A.\olomer Triphan-Spatli. Mohs. 



Description. 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). 

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

 even. Lustre vitreous, except on the face P, whicli 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 which solution an abundant precipitate is produced by oxalate of ammonia. 



Preimite 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 chabazitc or epistdbitc. 



Composition. Silica 43. CO, alumina 23.00, lime 22.33, oxide of iron 2.00, water 6.40 

 {Thomson). 



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

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



LOCALITIES. 



Essex County. Prchnitc occurs massive and seini-crystallized, and of a yellowish white 



