.Sect. VIIT.] 



MINERALOGY. 



227 



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*Q^>r 



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IC 



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b 



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It 



though the proportions of carbonic acid and lime are 

 precisely the same, the crystals ere hexagonal prisms. At 

 one time this very different crystalline stroctm^e was at- 



r 



tributed to the presence of a small per ceatage of car- 

 bonate of strontia (from 0'7 to 44) ; but as arragonite 

 has been found solely composed of carbonate of lime^ tl 





opinion seems abandoned. It has been lately stated that 

 when carbonate of lime is crystallized from a warm solu- 

 tion it takes the form of arragonite, and when from a 

 cold one that of com.mon calcareous spar. It should be 

 added, that the packing of the particles of arragonite 



is 



such that the specific gravity of this mineral is greater 

 than that of common carbonate of lime. 



At one time, though crystals of definite forms, constant 



internal strii"*:ure5 and chemical composition, allowing for 



isomorphous substitutions, were being obtained in a mul 



titude of chemical processes carried on upon the great 

 scale, as well as in the laboratory, much stress was laid 

 upon distinctions between artificial and natural products* 

 Now, however, that bodies, once only discovered in 

 various positions among rocks, have been formed arti- 

 ficially, sometimes by accident, at others by design, there 

 appears a disposition to look at inorganic matter more 

 generally, however convenient it may be to describe those 

 bodies by themselves which have been found in some 

 natural position. 



Among the researches which have tended to break 

 down the barriers once thought to exist between natural 

 and artificial minerals, the recent labours of M. Ebelmen 

 may be mentioned as the most remarkable, since among 

 the minerals produced are some commonly considered as 





