A. F. Rogers — Manganese Minerals. 147 



yellow distorted tabular crystals. It was identified 2 by 

 the index of refraction w = 1-723 =b -003 (recorded values * 

 n 7= 1-730; n/3= 1-729; a is perpendicular to the plates 

 so that w«'is not easily obtained). The plates are pale 

 yellow, non-pleochroic and give a biaxial interference 

 figure in convergent light. The optical determination 

 was checked by qualitative tests for aluminum, manga- 

 nese and water. 



Psilomelane. — Massive black and somewhat banded 

 psilomelane makes up the list of manganese minerals 

 that can be positively identified. Before it was broken 

 up to be used as manganese ore, the whole bowlder, or 

 so-called meteorite, was supposed to be psilomelane, but 

 it turns out that only the outside crust is psilomelane. 



Barite. — Barite seems to be practically the only min- 

 eral of the deposit which does not contain manganese. 

 It occurs in euhedral crystals along seams and in thin 

 sections, and it also proves to be interspersed through 

 many of the specimens. The euhedral barite crystals 

 are of two different habits: (1) highly modified crystals 

 of equant habit, with (110), (111) and (001) as promi- 

 nent forms and (2) crystals of pyramidal habit with the 

 unit bipyramid (111) as the dominant form, a very rare 

 habit for barite. 



Other minerals. — There are a few other minerals 

 which occur in such small quantities they have not yet 

 been identified. Some of the massive gray specimens are 

 apparently homogeneous but prove on microscopic exam- 

 ination to be microcrystalline aggregates. Mineralog- 

 ical literature is so full of descriptions of so-called new 

 minerals based upon such material that the writer has 

 refrained from an attempt to characterize these sub- 

 stances until better specimens can be obtained. 



Paragenesis of the Minerals. 3 



After the minerals of a rock or mineral deposit have 

 been identified, the next thing to do is to determine the 

 relations of the minerals to each other. This is often a 



2 This determination took only 15 minutes which is a testimony to the 

 value of optical methods in determining minerals in fragments by means 

 of the polarizing microscope. The writer had never seen ganophyllite 

 before and had scarcely heard of the mineral. 



3 By this term I mean the relation of associated minerals, not simply 

 the order of succession, which is only one phase of these relations. 



