SILICA. 289 



Orange county, to be hereafter described. The composition, by my analysis, was found to be 



as follows, viz : 



Silica, 51.35 



Oxide of iron and alumina, 14.40 



Lime, 24.25 



Magnesia, 9 . 36 



Near Kirby's graphite mine, four or five miles northwest of the village of Alexandria, 

 crystallized and lamellar pyroxene are found in considerable quantities. Colour dull green. 

 Cleavage seldom so perfect as in the specimens from Mount Defiance. It is associated with 

 graphite, sphene and scapolite. The crystals are usually low six or eight-sided prisms, with 

 the terminations highly modified ; but I have not found any of them sufficiently perfect for 

 measurement. They are generally imbedded in white scapohte. 



Pyroxene of a nearly black colour (black augite), is found associated with magnetic oxide of 

 iron at Crag harbour near Port Henry, on the innnediatc bank of Lake Champlain. It derives 

 its colour from the iron ore with which it is associated. It is usually in large irregular gi'ains, 

 firmly cemented, and sometimes in imperfect crystals. 



About half a mile north of Port Henry, the granular variety, of a light green colour, occurs 

 in white limestone. It is sometimes intimately mixed with the carbonate of lime, by which 

 its characters are somewhat changed. It is then less hard than pure pyroxene, and it effer- 

 vesces strongly in acids. This mixed mineral still has the cleavage and lustre of pyroxene. 

 In this we have an instance of those transformations which so frequently take place in the 

 mineral kingdom, and of which many examples occur in the hornblende family. 



At Willsborough, nine miles northwest of the village of Essex, granular pyroxene, (coc- 

 colite,) of a handsome green colour, occurs in a vein associated with granular garnet and 

 tabular spar. It is nearly transparent, has a white powder and a semi-vitreous lustre. Spe- 

 cific gravity 3.377. Fusible before the blowpipe into a dark opaque globule. The composi- 

 tion is as follows : 



Silica, „ 50.33 



Lime, 19.33 



Magnesia, 6 .83 



Protoxide of iron, 20.40 



Alumina, 1.53 



Water, „ 0.G6 



Protoxide of manganese, trace.* 



According to Dr. Emmons,t crystallized pyroxene is found on Long pond. He has noticed, 

 Pyramidi, with the faces o much extended in the direction of s; and the same with the faces 



* H. .Snybcrl. American Journal </ Science. V. IIG. t Nm-l'vrk Geological Reports, 1S37 



MiN. — PartII. 37 



