J. D. Dana on Pseudomorphism. 251 



The pseudomorphs of tin ore 7vith the form of felspar, 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 felspar at each end. Blum 

 makes mention of other specimens from St Just and Huel 

 Coates, which consist of granular quartz, and white mica, 

 with disseminated tin ore. These specimens are found in the 

 vicinity of the tin lodes of Cornwall, and appear to shew, 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 felspar porphyry of Altenberg, mentions that the rock 

 adjoining the lode is altered to horn stone mixed with granu- 

 lar quartz, and contains disseminated tin ore ; and also occa- 

 sionally includes masses of quartz and mica with more or 

 less tin. — J. D. D. American Journal of Science and Arts, vol. 

 xlviii., No. 1, p. 69. 



Observations on Pseudomorphism. By J. D. Dana. 



Notwithstanding the exact balancing of chemical formulas 

 which we find through Dr Blum's work, there is yet much 

 mystery with regard to the origin and formation of mineral 

 pseudomorphs. The elements removed and the amount added, 

 may be laid down with mathematical exactness, but that the 

 change has consisted in precisely such a removal and addi- 

 tion, is by no means sure. Moreover, in searching for the 

 causes of pseudomorphous changes, it appears to have been 

 too much the method to look for distinct causes for each se- 

 parate instance of pseudomorphism ; whereas we deem it pro- 

 bable that some few general principles will yet be ascertained 

 that will embrace and explain the whole subject. 



Although we cannot Iiope to remove all the obscurity that 



