4?70 M. Gustave Rose o?i the Formation 



mains quite unchanged, even if it be now re-immersed in water 

 or carbonate of ammonia, and allowed to stand in it for weeks. 

 In the same way, natural arragonite, which I had reduced to 

 a fine powder and treated in the same manner, did not in the 

 least change. 



2. Crystallization of Carbonate of Lime in the dry iscay. 



It is well known that carbonate of lime may under great 

 pressure and by great heat be brought to melt, and then on 

 cooling again it crystallizes. Sir James Hall performed this ex- 

 periment, and probably a similar process has frequently taken 

 place in the formation of the crust of the earth, since all marble 

 has originated in this manner. The fused lime at its crystal- 

 lization always forms calc spar, the three cleavage surfaces of 

 which are perfectly visible in the larger grains of the marble, 

 Arragonite is never produced in this way ; it occurs however 

 very frequently in the rents and cavities of mountain masses 

 which previously had evidently been in a state of igneous fusion, 

 as in basalt; but here the arragonite has evidently been formed 

 from the infiltration of a solution of carbonate of lime which 

 was heated by the still hot basalt, and therefore, according to 

 what we have stated above, the carbonate of lime deposited 

 itself as arragonite. 



Besides, arragonite cannot exist at all at a greater heat; for 

 if pieces of large arragonite crystals are exposed to a mo- 

 derate red heat, for instance in a glass tube over an alcohol 

 lamp, it puffs up, and falls, as Berzelius has shown, into a white 

 opake coarse-grained powder. No change takes place in the 

 chemical constitution at this merely moderate high tempera- 

 ture at which the arragonite pulverizes ; no gas is developed, 

 as Mitscherlich* has proved to be the case; and above all 

 things, it suffers scarcely any change in its weight, of which 

 I have convinced myself by several experiments; for 1-721 

 grammes of small fragments of crystals of arragonite from 

 Bilin in Bohemia, weighed, after having been heated, 1*717 

 grammes; and in a second experiment 1*9115 gr. weighed 

 1 *9090. The small loss in weight of 0*23 per cent, in the one, 

 and of 0*13 per cent, in the other case, arises only from somg 

 water of decrepitation, the escape of which on heating the 

 mineral evinces itself by the flying off' of small pieces. 



For the explanation of this phaenomenon, Haidingerf has 

 already advanced the opinion, that it should be ascribed to a 

 metamorphosis of calc spar into arragonite which takes place 

 at this higher temperature, and that the cause of the pulveri- 

 zing of the calc spar was this; that the carbonate of lime, in 



* Poggendorff's Annalen, vol. xxi. p. 157. t Ibid., vol. xi. p. 177. 



