58 Notices of Trappean Minerals. 



quite opaque* I have not observed any other form than that 

 usually figured. 



Datholite. — This mineral has been found in abundance at 

 Bergen Hill. It also occurs at Paterson, N. J., and at Piermont, 

 Rockland county, N. Y. It may generally be distinguished by 

 its high vitreous lustre. It is often associated with calcareous 

 spar, having a highly modified form. The action of an acid and 

 the blowpipe will of course readily decide the question. 



In the flame of a lamp datholite swells up like borax and be- 

 comes opaque, in which state it may be crushed by the fingers. 

 In hot nitric acid it is dissolved, leaving a siliceous jelly, which 

 adheres to the flask. The crystals are usually transparent or 

 translucent, but the forms are so highly modified as to baffle all 

 my attempts to figure them. 



Chabazite. — This is of rare occurrence at Bergen Hill, and the 

 crystals, which are in all cases of the primary form, are very mi- 

 nute. In one of my specimens, the rhombohedrons are an eighth 



of an inch in diameter. There occur at this locality small obtuse 

 rhombohedrons of calcareous spar, which might at first sight be 

 mistaken for chabazite. But the lustre and cleavage, independent- 

 ly of the chemical characters, will sufficiently distinguish them. 



The crystals are translucent or opaque, sometimes white, and 

 at others of a brownish tint. The edges and angles are some- 

 times rounded, as if they had undergone partial fusion subse- 

 quently to their formation. 



Prehnite. — It is abundant in various parts of New Jersey, es- 

 pecially at Paterson, Scotch Plains, and Bound Brook. About a 

 year since, Dr. Houghton, the geologist of Michigan, and my- 

 self, discovered a vein of prehnite in the trap on Bound Brook, 

 about eight miles northwest of New Brunswick, from which we 

 obtained an abundance of the mineral ; but the specimens do 

 not possess much beauty. It has been found at Bergeu Hill, but 

 not abundantly. I have also identified it in the greenstone at 

 Piermont, Rockland county, N. Y. 



Most of the specimens from New Jersey which I have exam- 

 ined, are of a light green color, and are made up of globular or 

 reniform masses, on the outer surface of which sections of crys- 

 tals both of the primary and secondary forms may be observed. 

 These crystals, however, are soon lost in radii which pass to the 

 centre. This radiated arrangement may be observed in almost 

 all the specimens. 



