Dr. Blum on Pseudomorphous Minerah. 73 



lime; CaSi+Mg^ Si^ (Pargasite) dropping Ca, thus becomes 



3[MgSi]. 



Steatite ivith the form of Dolomite. — These rhombohedral 

 pseudomorphs are found at Gopfersgriin. The change to stea- 

 tite is seen more or less complete also in the massive Dolomite. 

 Marlboro', Vt. is another locality of steatitic crystals of Dolomite. 

 Dolomite consists of carbonate of lime and carbonate of magne- 

 sia. The change consists in removing the lime and carbonic 

 acid, and substituting silica. 



Steatite with the form of Spinel. — This is a frequent pseudo- 

 morph in the granular limestone of Sussex County, N. J. and 

 Orange County, N. Y. In some crystals the change is incom- 

 plete, while others appear to be wholly altered to steatite. Those 

 of Newton, N. J, have a yellowish white or pale greenish color.* 

 The Tyrol near Dualta la Toja has afforded specimens of stea- 

 titic Pleonaste. The change here is a simple substitution of 



silica for alumina ; thus Mg Al becomes Mg Si. 



Steatite with the form of Quartz. — These pseudomorphs occur 

 at the same place at Gopfersgriin that affords the bitter spar crys- 

 tals above noticed. The form and strise of the planes are well 

 preserved. Where the change is partial, the quartz has become 

 white and without lustre; when complete, all the characteristics 

 of the quartz are lost except the external form, and a soft earthy 

 steatite has taken its place. 



Dr. Marx has suggested that the magnesia that caused the 

 change came from the bitter spar; but Dr. Blum urges in oppo- 

 sition to this view, that the magnesia in this mineral is in small 

 quantities and still remains in the bitter spar pseudomorphs, and 

 inclines to the opinion on the contrary that the quartz afforded 

 the silica that has altered the bitter spar. Several instances are 

 referred to of massive and columnar quartz in the same region alter- 

 ed to steatite, and also foliated quartz interlaminated with steatite 

 in consequence of a partial change. The striae of the surface 

 still retained show that the whole was originally quartz. 



* Prof. Beck in his report on the Mineralogy of New York describes the War- 

 wick crystals as black like spinels, — yet soft so as to be easily cut with a knife. 

 His analyses show that part of the spinel still remains. 



Vol. xLviii, No. 1.— Oct.-Dec. 1844. 10 



