58 



Case 62. 5573, colourless, with a brilliant lustre : the crystals form 



square plates.* 



Galejia, sulphide of lead : one o£ the commonest of metallic 

 minerals, and frequently found in ore deposits ; many of the 

 ores in the gold and silver cases consist of galena. The 

 specimens exhibited here are selected on account of their 

 showing crystal form or some other special characteristic. 



Galena commonly crystallises in cubes, the angles of which are 

 frequently truncated by faces of the octahedron (see fig. C, p. 72). 

 The cleavage is extremely perfect and ciibical. On tapping a piece of 

 crystallised galena with a hammer it will fly to pieces, each having 

 a cubical form and capable of being still further subdivided. The 

 characteristic cleavage can often be seen in hand specimens. 

 This, together with the leaden colour of the mineral and its streak, 

 and the ease with which it can be cut (sectU'dy), renders the 

 identification of galena exceptionally easy. 



1446, Broken Hill, and a cube cleaved from Boorolong galena 

 show the cubical cleavage well. 6535, in case 46, is a fine 

 specimen of the Boorolong mineral. 



Occasionally galena crystallises in eight-sided pyramids (ocfa- 

 Jiedra), this is shown by 9171 from Tingha District, and by 4191 

 (in case 46) from White Eock. 1059, Consols Mine, Broken 

 Hill: shows the cube and the octahedron occurring in combination, 

 as mentioned above. 



1074, Proprietary Mine, Broken Hill : a curious cauliflower- 

 like form. 



6697, Broken Hill, shows galena undergoing transformation 

 into carbonate of lead. (See above.) 



5565, Consols Mine, Broken Hill : galena partially replaced 

 by compounds of antimony with chlorine and vanadium. 



8418, Day Dream Mine, Barrier Eange: an earthy yellow 

 oxide of lead. 



For antimonial lead ores see Antimonv, case 68. 



-Sfigarcled as.a^di^tinct mineral species. 



