Dr. Blum on Pseudomorphous Minerals. 75 



fluor spar, mispickel, and wolfram, contains also steatitic topazes 

 engaged in quartz, part of which quartz is similarly altered to 

 steatite. The change commenced with the exterior. In one 

 crystal seen both ends are partially altered, while the middle re- 

 tained its usual transparency and hardness. The pycnite of 

 Zinnwald, Bohemia, is often changed to a greenish steatite. 



The change of the topaz requires the removal of 7A1, 2A1 PI', 



and the addition of 6Mg, by which (Al+2AlFl3)-i-6AlSi 



(topaz), becomes 6[Mg Si] or 6 of steatite. 



Steatite with the form of Feldspar. — Several localities are 

 stated, as Karlsbad in porphyry, Ehrenfriedersdorff in granite 

 along with lithomarge pseudomorphs of the same mineral ; near 

 Thiersheim in granite, with steatitic pseudomorphs of quartz. 



In the change, KSi-|-Al Si^ (feldspar) loses its potash and alu- 

 mina and receives 4Mg, making 4[Mg Si]. 



Steatite with the form of Mica. — At Monzoni, tabular crystals 

 of mica changed to steatite occur along with steatitic spinels. 

 At Briinn, the same occurs in a granite rock, the whole of which 

 is much altered — the feldspar to kaolin, and the brown mica to 

 a yellowish green steatite. The Thiersheim granite affords sim- 

 ilar changes. 



The rubellan from a wacke in Bohemia, is considered by Dr. 

 Blum a mica altered to a reddish brown steatitic substance. 



Steatite with the form of Scapolite. — The granular limestone 

 of Ersby and Pargas abroad, and Newton, New Jersey, have af- 

 forded these pseudomorphs. The change consists in removing 



from Ca^ 'Si+3A1 Si (scapolite), 3Ca, 3A1, and adding 4Mg, thus 



producing 4Mg Si. 



Steatite with the form of Augite. — Several localities are given 

 of these pseudomorphs in wacke, basalt, or porphyry, among 

 which are Eybenstock, Liitzelberg in the Kaiserstuhl, and Pozza 

 in the Tyrol. The crystals sometimes contain unaltered augite 

 within. In the Fassa valley, the variety Fassaite occurs altered 

 to steatite. Near Bilin in Bohemia, altered pyroxene is found in 

 gneiss. 



The Rensselaerite of Prof. Emmons is an interesting instance 

 of this change in northern New York, where it forms extensive 

 beds. 



