ZINC ORES. 83 



Only fusible on the edges when heated alone on the blow- 

 pipe. Dissolves in nitric acid. If roasted in a glass tube, 

 some of the sulphur is given off and a residue, zinc sulphate 

 (white vitriol), is left. Occurs with iron and copper pyrites, 

 silver ores, &c. Soluble in hydrochloric or citric acid. 



Silicate of Zinc (zinc glance]. 



Colour whitish, blue, brown, or green. 

 Not quite transparent 

 Streak whitish. 

 Lustre pearly or glassy. 

 H. 4-5 to 5 ; S.G. 3-3 to 3*5. 

 Contains about 53 per cent, of zinc ; the rest silica. 



Before B.F. froths up and gives a phosphorescent light. 

 Is fusible alone. With borax, yields a clear bead. If 

 heated in sulphuric acid it dissolves, and the solution 

 becomes gelatinous when cool : also in citric acid. 



Red Zinc Ore. 



Granular or massive. 



Cleavage brittle slices, rather like mica. 



Colour bright red. 



Streak orange yellow. 



Lustre brilliant. 



Not quite transparent. 



H. 4 to 4-5 ; S.G. 5 -4 to 5-6. 



Contains about 80 per cent. zinc. 



Infusible alone before the blowpipe. With borax, yields a 

 transparent yellow glass. Sol. in nitric or boiling citric acid. 



The principal ore, calamine, occurs in veins, beds, and 

 pockets, usually in limestone of Devonian, Carboniferous, 

 or Oolitic age. Zinc blende is found in the limestones of 

 Great Britain and elsewhere. It is often associated with 

 several metals in a lode. In Cornwall there is a saying, 

 " Black Jack rides a good horse ; " that is, where zinc 

 blende is met with at the top of a lode, copper may pro- 

 bably be met with deeper down. 



