446 A. F. Rogers — Manganese Minerals. 



weak double refraction, while the salmon-colored areas 

 showing cleavage are pleochroic from nearly colorless to 

 deep yellowish-red. The double refraction determined 

 by finding the thickness of a section from the highest 

 interference color of associated barite is about 0-04. 

 The direction of the cleavage traces in thin sections is 

 parallel to the slower ray which checks the optically 

 negative character determined above. 



The pyrochroite is also soluble in HC1 with the evolu- 

 tion of chlorine and gives abundant water in the closed 

 tube. 



Along cleavage planes the pyrochroite in thin sections is 

 seen to be altered to an opaque brown oxidation product. 

 This is a hydrous manganese oxide of some sort and may 

 possibly be the amorphous equivalent of manganite which 

 represent a higher state of oxidation of manganese than 

 pyrochroite. 



Rhodochrosite. — Ehodochrosite occurs both in euhedral 

 crystals along seams and in granular masses. The euhe- 

 dral crystals are pink in color and have the form of the 

 negative rhombohedron (0221), a common form for cal- 

 cite, but a very rare one for rhodochrosite. It usually 

 occurs alone, but in a few cases narrow faces of the posi- 

 tive unit rhombohedron (1011) were observed. The 

 rhombohedron (0221) was identified by the fact that the 

 cleavage rhombohedron truncates its polar edges. This 

 was checked by the following measurements made with 

 the simple reflection goniometer devised by the writer: 1 

 0221 A 2021 = 100° calc. = 99° 54') ; 0221 A 2021 = 80° 

 (calc. = 80° 6'). 



Some of the specimens are made up largely of fine- 

 grained reddish gray rhodochrosite which shows minute 

 cleavage surfaces. A few light reddish gray specimens 

 seem to consist of rhodochrosite and barite. Rhodo- 

 chrosite must be common in many specimens even when 

 not visible to the unaided eye, for they effervesce in hot 

 HC1 and thin sections show the presence of a rhombo- 

 hedral carbonate. 



Gano ph yll it e— -This very rare mineral, heretofore 

 known only at the original locality (Langban, Sweden), 

 was found along seams with cleavable barite as brownish- 



1 Science (n. s.) Vol. 27, p. 929 (1908). This little device constructed 

 out of a Penfield cardboard goniometer often saves the necessity of using 

 the large reflection goniometer when approximate measurements suffice. 



