THE NONMETALLIC MINERALS. 



253 



a Usually yields water in closed tube. 



The chemical relationship of the ores as found in nature is thus set 

 forth by Penrose: 1 



Manganese oxides frequently occur admixed in indefinite propor- 

 tions with the hydrous oxides of iron limonite, giving rise to the 

 manganiferous limonites as shown in Specimens Nos. 66090, 10867, 

 U.S.N.M. from Spain. 



FRANKLINITE. This may be termed rather as a manganiferous ore 

 of iron and zinc than a true ore of manganese. Nevertheless, as the 

 residue after the extraction of the zinc is used in the manufacture of 

 spiegeleisen, we may briefly refer to it here. The mineral occurs in 

 rounded granules or octahedral crystals of a metallic luster and iron 

 black color, associated with zinc oxides and silicates in crystalline lime- 

 stones, at Franklin Furnace, New Jersey. (Specimen No. 83941, 

 U.S.N.M.) It bears a general resemblance to the mineral magnetite, 

 but is less readily attracted by the magnet and gives a strong manga- 

 nese reaction. Its average content of manganese oxides Mn 2 O 3 and 

 MnO is but from 15 to 20 per cent. 



HAUSMANNITE. This form of the ore when crystallized usually takes 

 the form of the octahedron, and may be readily mistaken for franklin- 

 ite, from which, however, it differs in its inferior hardness, lower 

 specific gravity, and in being unacted upon by the magnet. (Specimen 

 No. 64241, U.S.N.M.) It occurs in porphyry, associated with other 



Annual Report of the Geological Survey of Arkansas, I, 1890, p. 541. 



