368 MINERALOGY 



tions giving the crystals the appearance of parallel growths or com- 

 plex aggregates ; also acicular, radiated, fan-shaped or in the form 

 of dendrites. 



Beautiful specimens are obtained in the Harz, Germany, where 

 it is associated with calcite. Manganite is a secondary mineral 

 formed much in the same way as limonite. Manganese is dissolved 

 out of the igneous or sedimentary rocks by percolating waters and 

 is carried in solution to be precipitated either as carbonate or oxide. 

 It is therefore a vein mineral, where it is associated with calcite, 

 quartz, and iron oxides, or it is found in nodules in clays and sedi- 

 mentary deposits. By dehydration manganite. passes into pyro- 

 lusite, which often retains the form of manganite. Small equidi- 

 mensional crystals of manganite are found at Salisbury, Connect- 

 icut, associated with the limonite. It also occurs in the Lake 

 Superior region; in Douglas County, Colorado. For use see 

 pyrolusite. 



Pyrochroite, Mn (OH) 2 , is isomorphous with brucite, see page 362. 



PSILOMELANE 



Psilomelane is an amorphous mixture of various hydrated oxides 

 of manganese and therefore varies greatly in its composition. It 

 generally contains barium oxide. One variety, asbolite, contains 

 cobalt, and another, lampadite, contains copper. 



Amorphous, botryoidal, stalactitic, reniform, or in crusts; 

 Color, black to steel-gray ; Luster, submetallic to dull and earthy ; 

 Streak, brown to black ; Opaque ; H. = 5.6, earthy varieties are 

 soft, soiling the fingers ; G. = 3.7-4.7. 



B.B. Like manganite, but usually contains barium or other 

 elements isomorphous with barium. 



General description. Psilomelane is associated with limonite 

 and they are both formed by the same agencies and under the same 

 conditions, so much so that all limonites will yield a qualitative 

 test for manganese, and in some cases the amount of manganese 

 may be considerable. 



Wad is the soft earthy form; it is also known as bog manganese 

 ore, as it is deposited from solution in many streams and marshes. 

 The pebbles in many streams are covered with a soft, velvety coat- 

 ing of amorphous hydroxide of manganese. These oxides also 

 occur as nodules on the floor of the ocean, where the oxides have 

 accumulated around some object, as a bone or shark tooth, as a 



