78 Mr HAIDINGER on the Parasitic Formation 



fibres being perpendicular to the surface of the specimens. When 

 the decomposition, which here only affects the form and ar- 

 rangement of particles, is allowed to proceed farther, crystals of 

 sugar-candy are formed in the space formerly occupied by a ho- 

 mogeneous mass which presented the most perfect conchoidal 

 fracture, and not a trace of crystalline structure. 



II. Changes dependent upon the presence of Water. 



HAUY'S Chaux sulfatee epigene, is a substance familiar to 

 every mineralogist, as it is found in great quantities, and is to 

 be met with in almost every collection. His view of it is per- 

 fectly correct : it was anhydrite, and is changed into gypsum, 

 by combining with a portion of water. The original cleavage 

 planes, still discoverable in the white, opake, and faintly glim- 

 mering masses, would give no argument of weight for uniting 

 the two species into one ; and yet considerations of this kind 

 have induced some mineralogists to join blue copper and mala- 

 chite into one species. These traces are not, however, produced 

 by cleavage, which is the mere tendency of the particles of anhy- 

 drite to separate more easily in certain directions than in others ; 

 but they are owing to actual fissures in the direction of the planes 

 of cleavage, visible in every fresh or not decomposed variety of 

 the species. On these fissures, and still more distinctly on some 

 larger irregular ones traversing the masses, distinct crystals of 

 gypsum are formed. Of the latter, I have seen several speci- 

 mens from Aussee in Stiria, in the collection of Gratz. The 

 decomposed individuals are much smaller in these than in the 

 varieties from Pesay in Savoy, described by HAUT. 



The absorption of water from the atmosphere, in saline sub- 

 stances, is usually attended with a solution of the latter in the 

 water so attracted ; that is to say, they deliquesce, and change 



