72 Dr. Blum on Pseudomorphous Minerals. 



in Saxony, at Heidelberg, near Rozena, and elsewhere. That 

 at Rozena is a red tourmaline, altered to lepidolite or reddish 

 mica. The Micarelle or Micanite of Neustadt is shown by Dr. 

 Blnm to be altered tourmaline, some of the crystals having dis- 

 tinctly the form of that mineral. 



Prehnite with the form of Analcime — These psendomorphs 

 occur at Dumbarton, at Molignon in the Tyrol, and near Wolfstein 

 in the district of the Lower Rhine. At the last locality they are 

 associated with calc spar and Datholite in Diorite. The Datho- 

 lite appears to have been partially acted upon at the time of the 

 change, and is supposed to have given the lime to the forming 



Prehnite. The change requires Na^* Si ^H-SAl Si ^+6H (anal- 

 cime) to have lost 3Na, 2Si,3H, and received 6Ca, by which 

 resulted 3[Ca=' Si+Al Si+H], or 3 atoms of Prehnite. 



Talc with the form of Kyanite. — These psendomorphs have 

 been observed at Wustuben, in the Fichtelgebirge. The edges 

 of the crystals are rounded and the surface is covered with a 

 thin crust of talc ; within they are a fine-grained aggregate of 

 talc, possessing the softness and other characters of this mineral. 

 The change consists in the substitution of magnesia for alumi- 

 na.* According to Dr. Blum, 2[AI2 Si] loses 4A1, and receives 



3Mg, and becomes thus Mg^ Si^ 



Talc with the form of Feldspar. — This pseudomorph has been 

 found at the tin mines of Altenberg in Saxony, associated with 

 quartz, specular iron, and light colored talc. The feldspar crys- 

 tals consist of talc in fine foliated grains ; they have a rough 

 drusy surface, yet tolerably sharp edges. The change consists 



in substituting 6Mg for K, Al, thus altering KSi+AlSi^ to 



2[Mg='Si2], or 2 of talc. 



Steatite with the form of Hornblende. — The Pargasite occur- 

 ring in granular limestone at Pargas, Finland, is sometimes alter- 

 ed to steatite of a greenish color. From the nature of the crys- 

 tals, Dr. Blum infers that the change commenced at the centre, 

 where it is most complete. It requires the removal only of the 



* The latest analyses make talc and speckstein (steatite) identical in composi- 

 tion, and lead to Mg Si as the formula of both. 



