340 MINERALOGY 



the natural oxide, occurring as it does with other manganese min- 

 erals, is colored by that element. 



The only deposit of zincite in the world of any importance is 

 at Franklin and Sterling, Sussex County, New Jersey, where it 

 forms an important zinc ore ; otherwise a very rare mineral. Here 

 it is intimately mixed with franklinite, willemite, and embedded 

 in calcite. Cleavable masses are common, which may also have a 

 lamellar structure. The crystals occur in isolated side stringers, 

 where the conditions of formation have differed from that of the gen- 

 eral body of the deposit, as these crystals are associated with such 

 rare minerals as leucophoenicite, pyrochroite and gageite. 



TENORITE 



Tenorite. Melaconite ; Black oxide of copper, CuO ; Cu = 

 79.8, O = 20.2 ; Triclinic ; a : b : c = 1.4902 : 1 : 1.3604 ; p = 80 

 28'; 100 A 110 = 55 46', 001 A 101 ; = 38 2', 001 A Oil ==53 

 18'; Forms, a (100), c (001), p(lll); Twinning plane, 001; 

 Cleavage, basal easy; Brittle, fracture conchoidal ; H. = 3-4; 

 G. = 5.85 ; Color, iron-gray to black ; Streak, black ; Opaque ; 

 Metallic. 



B.B. Fuses and in the R. F. on coal is reduced to malleable 

 copper. Other reactions as in cuprite. 



General Description. Crystals are rare ; small plates hexag- 

 onal in outline occur in the lavas of Vesuvius. Mostly occurs in 

 the black massive form, melaconite, or granular, earthy, and dis- 

 seminated. It is a common mineral occurring usually in small 

 quantities in the upper oxidation zone of most all copper deposits, 

 though not as common as the red oxide, cuprite. It is the ultimate 

 product formed in the oxidation of other copper minerals, as the 

 sulphides, native copper, and cuprite. 



Tenorite fuses at 1050 C., when it loses oxygen and forms cu- 

 prite. 



Other anhydrous protoxides of the formula of R"O, in nature, 

 are very rare and occur in localities in which there has been a pecu- 

 liar combination of physical and chemical conditions which has 

 favored their formation. 



Periclase, MgO, is an isometric mineral found in cubo-octahedrons 

 in the lavas of Vesuvius and also at Nordmark, Sweden. 



Manganosite, MnO, occurring at Langban, Sweden, and bun- 



