552 WATSON AND WHERRY: PYROLUSITE FROM VIRGINIA 



attack, through advanced stages in which only a few or many 

 scattered small fragments of residuary quartz remain, to the com- 

 pleted stage composed of all pyrolusite without visible quartz. 

 The partly replaced, fine-grained rock of blue-black color is 

 referred to locally as bluestone. 



In this connection it is of interest to note that similar replace- 

 ment of Cambrian quartzite by manganese oxide in the Virginia 

 part of the Piedmont Plateau province is well shown in hand 

 specimens and thin sections from the Myers manganese mine, 

 east of Lynchburg in Campbell County. Also the formation of 

 pyrolusite by replacement of quartzite in the Jubalpur district. 

 Central Provinces, India, has been described in detail by Fermor.^ 



Pyrolusite crystals measuring more than a millimeter across 

 are abundant at the Virginia locality in cavities and spacings in 

 both the ore and the rock. They vary in habit from tabular to 

 wedge-shaped, and frequently form closely interlocking aggre- 

 gates on the surfaces of joint planes, coatings on crusts of crystal- 

 line fibrous or columnar pyrolusite, and linings of small irregular 

 spacings in the blue-black ore; the latter appears amorphous to 

 the unaided eye, but much of it is seen to be minutely crystalline 

 granular under the magnifying lens. 



Of the large number of specimens tested, of both the crystals 

 and the crystalline mineral, all exhibited the physical and chemi- 

 cal properties of pyrolusite and none exhibited those of manganite. 

 Although careful search was made and numerous tests applied, 

 not a single specimen indicated the presence of manganite. 

 Without exception the crystals tested were soft, not exceeding 

 2.5 in hardness, and readily soiled the fingers. Color, steel 

 gray on fresh surfaces, black on other surfaces; luster, metallic; 

 and streak, black to slightly bluish black. Careful determi- 

 nations of the specific gravity gave 4.748 (crystals) and 4.885- 

 (crystalline) , values that correspond to those for pyrolusite and 

 are much higher than that for manganite. 



1 Fermor, L. Leigh. Memoirs Geo). Survey India 37: Ft. IV, pp. 811-814. 

 1909. 



2 Average of three determinations. 



