Mr. Vanuxem's Description of a Lamellar Pyroxene. 133 



to ascertain their nature. There are several cleavages, two 

 of which are parallel to four of the alternate sides of the octa- 

 gon, producing a prism with a rhombic base; these two 

 cleavages are not very easy to obtain, their surface being 

 rough, with but a feeble lustre ; the angles which these cleav- 

 ages form, as determined by the solid so generated, and the 

 measure of their corresponding faces in the crystals, are about 

 92° and 88°. This prism may again with ease be divided in 

 the direction of the smaller diagonal; the surfaces produced 

 are very smooth, and of considerable lustre ; this is the cleav- 

 age to which the mineral owes its highly lamellar structure. 

 In the direction of the larger diagonal, there are indications 

 of a fourth cleavage, but none parallel with the base. 



The lamellar masses rarely exceed two inches in their 

 greatest dimension, generally elongated and prismatic, of a 

 dark green colour with a tinge of yellow and bronze. The 

 shades of these colours frequently vary in the same specimen. 

 Scratches glass with ease ; fusible before the blowpipe into a 

 shining black globule. Specific gravity about S'24. 



To the result of the analysis * of the lamellar pyroxene of 

 West Point, is adjoined that of Delaware by Mr. H. Seybert, 

 in order to show the complete chemical identity of the two 

 minerals. 



West Point. Delaware. 



Silex 51-00 52-166 



Lime 21-00 20-000 



Magnesia 11-50 11*333 



Alumine 3-50 4000 



Deutoxide of iron with a) , , _._ ,^-r.o 



c > 11-53 10-733 



trace ol manganese J 



Water 1-00 1-266 



Loss 47 502 



100-00 100-000 



The mineral of West Point differs from hypersthene in the 

 angles given by their cleavages, which are different; those of 

 hypersthene being as the numbers 100, 80, and 50; and also 



* The analysis of the mineral was made in the following manner, having 

 previously ascertained that it was composed of silex, lime, magnesia, alumine, 

 and oxide of iron, with a trace of manganese: — Pulverised and calcined a 

 portion of the mineral for water; fused another portion with potash in order 

 to decompose the mineral ; dissolved the whole in nitro-muriatic acid, then 

 evaporated to dryness ; added acidulated water, and filtered, this gave the 

 silex; precipitated the metals and alumine by hydrosulphate of ammonia; 

 separated the alumine by potash ; threw down the lime by oxalate of potash, 

 and obtained the magnesia by boiling the liquor with potash. 



in 



