244 Dr J. Reinhard Blum on Pseudomorphous Minerals. 



riably obtained by digging down sixty or one hundred feet 

 from the surface. The same has been observed by Alberti 

 in the Muschelkalk of Germany. This change consists 

 merely in the addition of water, and the facts cited evince 

 that it takes place principally through atmospheric agency. 



Chalcedony with the form of Datholite. — According to Levy, 

 the chrystallized chalcedony from Hay-Tor, Devonshire, 

 called Haytorite, is altered Datholite. The change consists 

 in the removal, from the compound, of lime, boracic acid, 

 and water, and the addition of silica. 



Lithomarge rvith the form of Topaz. — Topaz altered to 

 lithomarge occasionally occurs in Brazil in a talcose slate, 

 and a Siberian specimen has been observed with a milk- 

 white exterior, owing to a similar change. The change con- 

 sists in the removal of fluoride of aluminum and the addition 

 of water. 



Kaolin tv'ith the form of Felspar. — This very frequent change 

 requires only the most common agents. Forchammer has 

 shewn that heated water, even when pure, will cause the 

 alteration; but Dr Blum is disposed to consider carbonic 

 acid as usually present when it is in progress, and alludes 

 to instances of regions of carbonated waters where the pro- 

 cess goes on with unusual rapidity. 



Mica with the form of Andalusite. — Crystals of andalusite 

 have been observed changed wholly to a light-coloured mica, 

 and others in which this change was but partially complete, 

 the ends being mica and the middle andalusite. In the 

 change, silica and potash are added. 



Mica with the form of ScapoUte. — Dr Blum describes a 

 crystal of scapolite altered to mica, from Arendal, which is 

 three inches long, and consists of an aggi-egate of mica 

 scales. Along with the altered scapolite there is a soft talc- 

 like mass, which also appears to have been produced by the 

 alteration of this mineral. 



Mica with the form of Tourmaline, — Crystals of tourmaline, 

 consisting of mica, or with mica terminations, have been ob- 

 served in Saxony, at Heidelberg, near Rozena, and else- 

 where. That at Rozena is a red tourmaline, altered to lepi- 



