102 Mr HAIDINGER on the Parasitic Formation 



yellowish-white faintly translucent matter, as appears from the 

 delineation of colours, was completed by a brownish opake mat- 

 ter, in the shape of the combination R 1 . R + oo, the form 

 dode'caedre of HAUY. These brown portions have also a carious 

 aspect, as from decomposition, and are studded with small crys- 

 tals of heavy-spar, of the same kind as that which replaces the 

 crystals of witherite. 



VIII. Changes in Minerals containing Antimony. 



The chemical changes of the minerals containing antimony 

 have not been sufficiently attended to. It is certain that the na- 

 tive antimony takes up oxygen, and then presents a white opake 

 mass, shewing every peculiarity, in respect of form, of the original 

 substance, as I have seen in a specimen in the museum at York. 

 This is probably the oxide of antimony. The prismatoidal anti- 

 mony-glance consists of sulphuret of antimony, a mixture of one 

 atom of the metal and three atoms of sulphur, Sb S 3 , the ratio of 

 antimony and sulphur being 72.77 and 27.23. It is converted by 

 decomposition into a yellowish opake mass, of an earthy aspect, 

 which is proved by experiments with the blowpipe still to con- 

 tain a notable quantity of sulphur, beside water and antimony. 

 In this case the form is preserved. Sometimes, however, as at 

 Braeunsdorf in Saxony, the decomposition is complete, and at- 

 tended with change of form, in the same manner as the lead- 

 glance. The decomposition begins from the surface, which is 

 corroded, and becomes perfectly smooth. In the cavities thus 

 produced, crystals of the antimony-baryte are deposited, which 

 consist of pure oxide of antimony, one atom of the metal com- 

 bined with three atoms of oxygen, or Sb, the two ingredients be- 

 ing in the ratio of 84.32 to 15.68. Each atom of sulphur is ex- 

 actly replaced by an atom of oxygen. 



