50 PHYSIOGRAPHY. CLASS i. 



blowpipe, hut is difficultly fusible, if its water of crystalli- 

 sation has been driven off. 



3. It effloresces from several rocks, both in their original 

 repository, and in artificial walls, and then it is a product 

 of their decomposition. It forms the principal ingredient 

 of certain mineral waters. 



4. It occurs in Freiberg and in its neighbourhood efflo- 

 rescent upon gneiss, in several places of the Hartz, in 

 Scotland, in Berchtesgaden, in Salzburg, at Idria in Car- 

 niola, from whence it has been described under the name of 

 Halotrichum, or Hair-salt, in Bohemia, in Hungary, &c. 



5. After having been purified, it is employed in medi- 

 cine, as also for the production of magnesia. 



GENUsVIII. ALUM-SALT. 

 1. OCTAHEDRAL ALUM-SALT. 



Octahedral Alum. JAM. Syst. Vol. III. p. 27. Man. p. 17. 

 Alum. PHILL. p. 196. Alaun. Hoffiii. H. B. Th. 

 IV. 2. S. 169. Alaun. HAUSM. III. S. 813. Alaun. 

 LEONH. S. 625. Alumine sulfate'e alcaline. HAUY. 

 Trait^, T. II. p. 387. Tabl. comp. p. 22. Alumine 

 sulfate'e. Traite, 2de. Ed. T. II. p. 114. 



Fundamental form. Hexahedron. Vol. I. Fig. 1. 

 Simple forms. H (r); 6 (P) Vol. I. Fig. 2. ; D (o) 



Vol. I. Fig. 81. ; B Vol. I. Fig. 33. ; Ci Vol. I. 



Fig. 34. 



Char, of Comb. Semi-tessular with parallel faces. 

 Combinations. 1. H.O. Vol. I. Fig. 3. and 4. 



2. H. O. D. 



3. ILO. D. B. Ci. 



Cleavage, octahedron, imperfect. Fracture con- 

 choidal. Surface smooth. The faces of the 



