SILICA. 297 



APPENDIX. 



Steatitic-Pyroxene — Rcnsselaerite of Dr. Emmons. Before leaving Pyroxene, I must 

 introduce a notice of what I consider to be a variety of it, described by Dr. Emmons as a 

 distinct species.* 



Description. Colour white, yellowish or greyish white, and dark. Occurs in soft cleava- 

 ble masses, the primary form of which is an oblique rhombic prism. M on M' 94° 00'; P on 

 M 106° 30', according to Emmons. By my measurement of the white variety, its angles do 

 not differ from those of pyroxene (Fig. 192). Fracture uneven. Opaque. Hardness from 

 3 . to 4 . 0. Specific gravity 2 . 874. Before the blowpipe, it fuses with difficulty into a white 

 enamel. 



Composition. According to my analysis, the composition of a specimen from Canton in 

 the county of St. Lawrence, is as follows, viz : 



Silica, .59.75 • 



Magnesia, 32 . 90 



Lime, 1 . 00 



Peroxide of iron, 3. 40 



Water, 2.85 



The above results agree very well with those obtained from some varieties of what Beudant 



calls Steaiitic Pyroxenes from Sahla, and which contain variable proportions of foreign matter. 



This author quotes three analyses of Rose, the composition of one of which is as follows : 



Silica, 60.65 



Lime, 4 . 97 



Magnesia, 25.20 



Protoxide of iron, 4.18 



Oxide of manganese, 0.78 



Water, 4.38 



This substance has the form and cleavage of pyroxene. According to calculation, it contain.*! 

 pyroxene 37.40, steatite 62.30, hygrometric water 0.40.t 



I have little doubt that the mineral in question is a mixture of a similar kind. The steatite 

 to which it owes its somewhat soapy feel, and its softness, has been intruded into it without 

 disturbing the crystalline form of the pyroxene. What has caused this partial decomposition 

 of the pyroxene, and the intrusion of the foreign matter, is not so easy to determine. Cases 

 of a similar kind arc, however, by no means rare, especially in the species hornblende, and 

 even in spinelle, as will be hereafter noticed. 



* Nai'-York Geolnpcal Reports, 1837. ' t Beudant. Trmle Elhnentatrt dt Minlratogie. 1.224, 



Mix. — P.vKT II. 38 



