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. 



Serpentine with the form of Aug'ite. — 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 removal of 3Ca from Mg^Sis-}- 



Ca^ Si2 (augite), and the addition of 6Mg, 6H, thus affording 



2Mg3Si2+3MgH2 (serpentine). 



Serpentine 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='Si2] remove 4Ca and add 15Mg, 18H, 



and we have 3[2Mg3 Si=^ +3MgH2], 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 Poggendorf's 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'^ Si«) remove 3Mg and add 6H, and 



we have 2Mg3 Si^+SMgH^ the formula of serpentine. The 



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

 Water therefore is the only agent required in this change, though 

 carbonic acid may be presumed to aid, as the gangue 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 (Mg5 -)- Fe^) 3 Si ; 4 atoms of which contain Mg9-|-Fe3-|-Si4 ; tothisadd 



the 6H! and remove the Fes, and we have without other change simply serpen- 

 tine as ahove. — D. 



