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NEW YORK STATE MUSEUM 



Zincite (red zinc ore) ZnO 



This oxid of zinc contains 19.7$ oxygen and 80.3$ zinc; it 

 usually carries some manganese. 



The natural crystals, which are rare, have been referred to 

 the hemimorphic group of the hexagonal system. Zincite ordi- 

 narily occurs in deep red to brick-red adamantine masses with 

 a foliated or granular structure or as coarse grains dissemi- 

 nated through the matrix. It has a subadamantine luster and 

 is translucent. 



Zincite occurs in the vicinity of Franklin N. J. associated with 

 the minerals characteristic of that locality and is mined with the 

 associate minerals for the zinc which it contains. 



Corundum (emery) A1 2 3 



Corundum is alumina, or sesquioxid of aluminium, and con- 

 tains 47.1$ oxygen and 52.9$ aluminium; massive emery contains 

 more or less iron oxid as an impurity. 



Crystals of corundum are rhombohedral (fig. 186, 187); rough 



Fig. 186 



Fig. 187 



Corundum 



and rounded forms are characteristic, as well as twinning, 

 which is indicated by laminated structure and intersecting 

 striations. With the exception of the diamond, corundum is 

 the hardest substance known. 



The precious varieties known as sapphire and ruby are trans- 

 parent or translucent, with vitreous to adamantine luster, 

 and abound in fine colors. 



The gems cut from these varieties are: 



Sapphire. Blue in color 



Oriental rubv. A rich red 



