310 DESCRIPTIVE MINERALOGY. 



to Necker.) Fracture uneven. Lustre bronze-metallic upon the most perfect diagonal clea- 

 vage ; in other directions, more or less vitreous. Opaque or slightly translucent on the edges. 

 Hardness 6 . 0. Specific gravity from 3 . 338 to 3 . 385. Before the blowpipe it is infusible 

 per se, but melts upon charcoal into a greenish grey opaque globule ; v»rith borax, it melts 

 into a greenish glass. It is unacted on by acids. , 



Composition. Specimen from Labrador — Silica 54.25, magnesia 14.00, alumina 2.25, 

 lime 1 .50, oxide of iron 24.50, water 1 .00 [Klaproth). It is therefore a silicate of magnesia 

 and iron. 



Geological Situation. It is usually found in primitive rocks, especially those of a gra- 

 nitic character. It has also been observed in greenstone. 



It may be here remarked, that there is some uncertainty in regard to this mineral. Dr. 

 Kohler of Cassel, some years since, examined several varieties of diallage, and inferred 

 from his analyses that metalloidal diallage, bronzite and hypersthene, are subspecies of 

 pyroxene, and not, like schiller spar and anthophyllite, species of the schiller spar family.* 

 Among these analyses, that of the metalloidal diallage approaches more nearly that of our 

 so called hypersthene from Lake George, to be presently noticed, than any other. Mr. J. 

 Phillips expresses the opinion that hypersthene and diallage often differ from each other 

 rather by the crystalline arrangement of the parts, or the substitution of mutually replacing' 

 substances, than by any essential and constant characters.! 



LOCALITIES. 



Essex County. According to Dr. Emmons, hypersthene is very abundant in what are 

 termed the granite rocks of this county. It is associated with labradorite. He does not 

 decide whether it is identical with the hypersthene rock of Dr. MacCulloch ; but he says it 

 is as truly one of the constituents of this rock as mica or quartz in the common granite, 

 though not so generally diffused. He also slates that the most valuable beds of magnetic iron 

 ore in Essex, and the other northern counties, occur in hypersthene rock.| 



Washington County. A specimen which was obtained from the banks of Lake George 

 in the town of Putnam, and about two miles from Ticonderoga, closely resembles the so 

 called hypersthene from the more northern counties. Its colour is from ash-grey to black. 

 It is foliated and lamellar, and has a pearly or metallic lustre on the cleavage faces. The 

 streak is white. Its hardness is less than that of pyroxene. 



The following are the constituents of this mineral, viz : 



Silica, 45. 45 



Lime, 24.33 



Magnesia, 18.00 



Oxide of iron, 11.49§ 



* Brewstir's Edinhirjih Journal of Science. IX. 361. ^Phillips Geology. II. 63. 



i Emmons. New-York Geological Reports, 1838 and 1840. 



^ The above mineral exactly resembles the so cnlled hypersthene fiom near Wilmington, Delaware. The latter is magnetic. 



