SILICA. 



295 



Fig. 217. 



Fig. 218. 



<J 



M 



1^ 



U 



" ' -^ , 



M 



Fig. 219. Strewed over with loose fragments 



of crystals. They are usually of 

 the form represented in Fig. 217, 

 which is the perihexaedre of Haiiy> 



ji)M| r |m I .jyjfjj tijg fjjgg f. much extended, and 



the other faces very narrow, so as 

 to give the crystal the appearance 

 of a flattened table. 



Near Knapp's quarry, twin crys- 

 tals of white pyroxene have been obtained, the composition of which will be understood from 

 an inspection of Figs. 218 and 219. They closely resemble the compound crystals of albite. 

 Rockland County. At the Horsenclever iron mine, in the town of Haverstraw, fine spe- 

 cimens of the lamellar variety are found, which closely resemble hypersthene. 



St. Lawrence County. About a mile southwest of the village of Gouverneur, there is 

 a locahty of crystallized pyroxene of a light grey colour. The forms are the primary, and an 

 eight-sided prism, but they are usually without terminations. They are associated with crys- 

 tallized hornblende and dark green coccohte, and occur in white limestone. 



In the town of Rossie, two miles north of the village of Oxbow, crystallized pyroxene 

 occurs in an aggregate of feldspar, apatite, crystallized hornblende and sphene. It is of a 

 green and greyish green colour. Large crystals have been obtained at this locality. They 

 are usually of the primary form (Fig. 192), and the modifications Figs. 207 and 208. 



Fig. 220. 



Fig. 221. 



Near De Long's mill, in the town of Hammond, crystal- 

 lized pyroxene of a dark colour occurs along with zircon, 

 feldspar and apatite. The forms are six and eight-sided 

 prisms with four terminal planes, represented in Figs. 220 

 and 221. M on a; 134° 17'; Zona; 114° 26'; a: on a; 131° 

 8'. 



Lamellar p3rroxene, of a white and greyish white colour, 

 is found in abundance near the village of Richville in the 

 town of De Kalb. It cleaves Uke most of the varieties, but 

 it is often softer than is usual with this mineral. I attribute 

 this to its mixture with serpentine, and it probably belongs to that variety which I call steati- 

 tic pyroxene, to be presently noticed. It is associated with tremolite and brown tourmaline, 

 the whole contained in white limestone. 



Washington County. In the town of Putnam, on the bank of Lake George, about two 

 miles south of Ticonderoga, there are beautiful specimens of lamellar pyroxene. The colour 

 varies from grey to nearly black, and some specimens have a high pearly lustre on the faces 

 of cleavage, while others have a metallic lustre. It is both foliated and lamellar ; and the 

 folia, which are sometimes waved or bent, may be obtained of the size of the hand. The 

 latter variety is apparently less hard than is usual with this mineral, but this is probably owing 

 to its structure. 



