ON SPURIOUS CRYSTALS. fj^ 



never yet been observed in the quartz itself. All these pseuHo- 



morpboscs of steatite and serpentine are so many examples 



added to the well-known instances of quartz, jjrhich borrows 



sometimes from one species, sometimes from another, forms it 



is incapable of assuming when left to itself. 



The idea that first occurs to the mind respecting the origin Supposed on- 



of such accidental forms has been to suppose, that the spe- S'"- 



cies, which has lent its forai, has had an influence on the crys- That a portion 



tallizdtion ; and though mixed with a foreign substajice, often imitateZhas 



predominant in point of quantity, nevertheless acts the princi- been able to 



, , . , . 1 • 1 1 , .1 ,• • • dafermine the 



pal part, and impels its companion to yield to the form it im- form of the 



poses on it. Thus it was at first supposed, that, in the rhom- substance 



., , . . ., , ,. , , •, • , mixed with it. 



boidal hgures, similar to those ot calcareous spar, exhibited 



by the steatite of Bayreuth, and the same might be said ot 

 the other forms imitated from carbonate of lime, there existed 

 originally a certain quantity of carbonate of lime, as in the 

 crystallized sandstone of Fontainebleau, and that the steatite 

 owed its form to this carbonate. 



Subsequently however the pseudocrystals of steatite have But the false 

 been compared with the steatitic mass, by which they are '^'Tstal does 



11 1 , 111 1 r 1 i , ""^t: appear to 



completely envclojjcd ; and they have been tound pertectly cont^ia any 



similar in every respect to the gangue in which they occur, ^^^^^ i'^itioa. 

 possessing its softness, greasy appearance, soapy feel, &c. No 

 trace of the substance, the presence of which was supposed 

 necessary to imprint on it the regularity of form that distin- 

 guishes it, could be perceived. These considerations, and Difficulttoex- 

 the difficulty of explaining how carbonate of lime, hyalin P^^^"^^"^^^^^-^' 



1 r- 1 1 I 1 • , . , ^^^^ should 



quartz, and feldtspar, could yield their place to the steatitic take the piac« 



particles, allowing them to arrange themselves in the precise ?^ ^ preexist- 



in*'' cfvsta.1 * 

 order required for the. regularity of the figures retained, have 



appeared a motive sufficient to consider these forms as proper hence suppos- 

 to the substances bearing them. Analogy, however, and the '^^.^'^ ^^ ^'^ 

 usual laws of crystallization, appearing to me little favoura- crystal. 

 blc to this opinion, I shall submit my doubts on the subject 

 in a few words. 



We frequently see quartz assume the cubic or octaedral Spurious crys- 

 form of fluate of lime, at others affect that of the metastatic tals of quurt/. 

 carbonate of lime, and again put on several of those of sul- 

 phate 



