﻿76 Dr. Blum on Pseudomorphous Minerals. 



Much that is interesting might be cited respecting the steatitic 

 pseudomorphs of tourmaline, staurotide, garnet and idocrase; but 

 we pass on to the serpentine pseudomorphs. 



terpentine with the form of Augite. — Near Schwarzenberg 

 in Saxony, a serpentine occurs with the form of Sahlite, which 

 was taken for crystallized serpentine, until aftewards shown to 

 have the angles of the latter mineral. A black augite altered to 

 serpentine has been found at Fahlun, 



The change requires the 



t • 4 



• f * 



;a from Mg 3 Si 9 -f 



| 



6H, thus affording 



• • • 



H 



Serpe?itine with the form of Hornblende. — Crystals of actino- 

 lite altered to serpentine have been observed near Presnitz, in 

 Bohemia, and hornblende crystals at Easton, New Jersey. The 

 graywacke of Plauen, Weischlitz, and Geilsdorf, affords other 

 localities of these hornblende pseudomorphs. 



• • • » * - • 



From 4[CaSi+Mg 3 Si 2 ] remove 4Ca and add 15Mg, 18H 



* ■ 4 



and we have 3[2Mg 3 Si 2 + 3Mg H 2 ], or 3 atoms of serpentine. 



Serpentine with the form of Olivine. — Q,uenstedt has shown 

 that crystals of serpentine from Modum in Norway, have the 

 form of olivine, and in Poggendorfs Annalen for 1835, explain- 

 ed the chemical changes passed through in turning olivine into 

 serpentine. Some of the crystals are four inches long; they 

 usually have rounded angles and little lustre. The change he 

 explains as follows : — 



From 4 of olivine (Mg " 2 Si 4 ) remove 3Mg and add 6H, and 



we have 2Mg* Si 3 +3MgH 



The 



Fe (iron) in the olivine is supposed to be removed with the 3Mg.* 



Water 



carbonic acid may be presumed to aid, as the gangne contains 

 bitter spar. Tamnau has objected to this origin of these ser- 

 pentine crystals on the ground of the extensive changes that 

 must have been required in producing the wide-spread beds of 



* If the iron in the olivine is to the magnesia as 1 to 3, the formula of olivine 

 is then (Mg? + Fei) 3 Si ; 4 atoms of which contain Mg»+Fe3+Si4 ; to this add 



the 6H and remo\ 



tine as above. — D. 



