608 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 47. 



The material shows a deep brown nodular crust up to 5 mm. 

 thick, and fiat radiations up to 1 cm. in diameter, on the surface of 

 an iron-stained quartzite. In some specimens it bears implanted 

 globules of psilomelane, yellow needles of cacoxenite, and powdery 

 clay. Internally the crusts are coarsely fibrous, -with, the fibers 

 perpendicular to the surface, and the material was evidently origi- 

 nally a gelatinous precipitate, which has become hard and crystalline 

 in place, thus representing a "meta-coUoid," as defined by the 

 writer in a recent paper.* 



After a preliminary analysis (1) had shown the general nature of 

 the mineral, material for further study was obtained by crushing 

 selected fragments, and the powder looked completely crystalline 

 and homogeneous under the microscope, except for the presence of 

 a trace of clay or fine sand. Standard methods of analysis were 

 used, the iron being determined with permanganate, the manganese 

 by the bismuthate and the Ford methods, and the phosphorus weighed 

 as magnesium pyrophosphate after separation by molybdate. A 

 small amount of water — less than 0.5 per cent — was given off below 

 100°, and the alialyses were made on coarsely powdered material 

 dried at this temperature, for the fineness of the grinding and the 

 humidity of the air were found to have a distinct effect on the water 

 content. 



Table of analyses. 



1. Analysis by J. S. Long. 



2. Analysis by Louis H. Koch. 



3. 4. Analyses by the writer. 



5. Average of the preceding, uniting FejOs and MnjOa, which are evidently isomorphous. 



6. Same, corrected by removing the SiOeand recalculating to 100°. Ratios, R203:Pj06:HsO=1.82:l:3.47. 



7. Partial analysis of the associated psilomelane, by Mr. Long. Alkalies and alkaline earths present but 

 not determined. 



These analytical results apparently do not indicate any simple, 

 fixed formula for the mineral, nor do they establish its identity with 

 any previously described species; although inspection of the analy- 

 ses, and the formulas derived from them, of the various ''species'' 

 of ferric phosphates in Dana's System, shows that similar difficulties 

 have been encountered in this group of minerals before. The Heller- 

 town mineral agrees in specific gravity and optical properties, how- 



iJourn. Wash. Acad. Sci., vol. 4, 1914, p. 112. 



