250 Dr J. Reinhard Blum on Pseudomorphous Minerals. 



quartz. Implanted crystals are thus altered when there are 

 no moulds to be filled up. 



Another kmd still, proceeds from the incrustation of 

 crystals by another mineral, and their subsequent removal, 

 leaving a thin hollow mould, with the external and internal 

 form of the original crystal. 



The various siliceous pseudomorphs are the most numerous 

 and most interesting of this class. We have already enu- 

 merated them on page 242. The change is often complete 

 through the crystal, the whole being altered to quartz. In 

 other instances, the interior is vacant, or consists of the ori- 

 ginal mineral still unaltered. Crystals of fluor-spar, consist- 

 ing of quartz, except a small fluor nucleus, are noticed by 

 Blum. An instance is given by our author of altered calc- 

 spar, in which the silica penetrated between the laminae, 

 forming a series of plates, and the remaining lime afterwards 

 removed, left a cellular crystal with the general structure of 

 the calc-spar. Their surfaces are generally rough or drusy, 

 but sometimes are smooth, with the edges and angles sharp. 



Besides the siliceous pseudomorphs, others of special in- 

 terest, are those of felspar, with the form of calc-spar ; silicate 

 of zinc, with the form of calc-spar, and other minerals, above 

 enumerated ; of tin ore, with the form of felspar ; peroxide of 

 iron, with the form of calc-spar ; brown iron ore, with the form 

 of heavy-spar, fluor-spar, calc-spar, bitter-spar, quartz, &c. 



The account of the changes of calc-spar to silicate of 

 zinc, are interesting. "When complete, the crystals con- 

 sist wholly of granular silicate of zinc, with the interior 

 forms, but never hollow. When less complete, zinc has in- 

 crusted and penetrated between the cleavage, laminae of the 

 lime, some of the latter being yet included. The silicate of 

 zinc, which has here produced those pseudomorphous changes, 

 appears to have, in part, proceeded from zinc-blende in the 

 vicinity. Dr Blum supposes the first change to have been to 

 sulphate of zinc, and then, through the action of siliceous 

 waters, to a silicate, the sulphuric acid going, at the time, into 

 combination with lime, and forming gypsum, a mineral ob- 

 served by Zimmermann at the locality. 



