438 



Scientific Geology. 



I have observed only one modification of this crystal, and that con- 

 sists of a slight truncation on the acute lateral edges, as represented 

 in this figure. (No. 1202.) 



The height of the prism is about equal to the longest edge. It 

 yields to mechanical division only parallel to the bases. It has a lus- 

 tre somewhat pearly on the cleavage plane, and not unfrequently the 

 folia are slightly curved. It is always white or colorless ; sometimes 

 transparent, but generally only translucent. In every other charac- 

 ter it corresponds with Heulandite and stilbite. On hot coals it 

 whitens, and before the blowpipe melts into a white spongy enamel. 



The crystals of this mineral, (and I am not sure that it ever occurs 

 except in crystals,) are mingled, usually in the least proportion, with 

 crystals of chabasie ; either in the amygdaloidal cavities of the green- 

 stone, or in its fissures. I have rarely met with a crystal whose long- 

 est side exceeded the tenth of an inch : and most of the specimens 

 in the collection will need a microscope for their examination. It is 

 very rare and obtained with difficulty, though small specimens will 

 reward the persevering collector. (Nos. 1200 to 1204.) 



At the same spot in Deerfield a radiated mineral occurs, forming 

 sometimes perfect spheres, of the size of an ounce bullet, which may 

 be Lincolnite, though more probably it is stilbite. 



This same radiated mineral is found at Bellow's Falls in Vermont, 

 encrusting gneiss. On examining some specimens which I obtained 

 there a few years ago, I perceive several distinct crystals of Lincoln- 

 ite, which are quite small. 



It is obvious from the preceding description, that this mineral differs 

 from stilbite and Heulandite, only in its crystalographical characters. 

 Stilbite crystalizes in a right square prism. Heulandite comes nearer 

 to Lincolnite ; its primary form being a right oblique angled prism. 

 But the angles of its bases are about 50 and 130; differing 10 from 

 those of Lincolnite. Such a difference cannot be imputed to the im- 

 perfection of mensuration ; nor can I conceive how it could possibly 



