80 Dr. Blum on Pseudomorphous Minerals. 



Besides the siliceous pseudomorphs, others of special interest 

 are those of feldspar with the form of calc spar, silicate of zinc 

 •v^ith the form of calc spar and other minerals above enumerated, 

 of tin ore with the form of feldspar, peroxyd of iron with the 

 form of calc spar, brown iron ore with the form of heavy spar, 

 flnor spar, calc spar, bitter spar, quartz, &c. 



The account of the changes of calc spar to silicate of zinc are 

 quite interesting. When complete, the crystals consist wholly of 

 granular silicate of zinc, with the interior porous but never hol- 

 low. When less complete, zinc has incrusted and penetrated 

 between the cleavage laminae of the lime, some of the latter 

 being yet included. The silicate of zinc which has here produced 

 these 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 wiih lime and forming gypsum, a 

 mineral observed by Ziramerraann at the locality. 



The pseudomorphs of Tin Ore with the form of Feldspar, 

 come from the mine of Huel Coates in Cornwall. They are 

 mostly compound crystals with a rough exterior, and consisting 

 of granular tin ore more or less mixed with granular quartz. 

 Anker has described similar pseudomorphs which are tin ore in 

 the middle and pure unaltered feldspar at each end. Blum makes 

 mention of other specimens from St. Just and Huel Coates, 

 which consist of granular quartz and white mica with dissemin- 

 ated tin ore. These specimens are found in the vicinity of the 

 tin lodes of Cornwall, and appear to show as Dr. Blum states 

 that the gangue of the ores was produced by the same process 

 that formed these pseudomorphs. Von Dechen, in an account 

 of the tin ore occurring in the syenite and feldspar porphyry of 

 Altenberg, mentions that the rock adjoining the lode is altered to 

 hornstone mixed with granular quartz, and contains disseminated 

 tin ore ; and also occasionally includes masses of quartz and mica 

 with more or less tin. J. D. D. 



