204 Brush and Dana — Mineral Locality at B ranckville. 



finding again. It has also afforded another new member of 

 the triphylite group, a sodium-manganese phosphate, which we 

 shall call natrophilite. Besides this we have identified another 

 phosphate of manganese, and one which from the first we had 

 hoped to find, viz : the rare mineral hureaulite, thus far only 

 certainly known from Limoges, Commune of Hureaux, in 

 France. 



The general method of occurrence of the phosphates of 

 manganese is such as to confirm the opinion that we have 

 expressed in a former paper, that the manganesian triphylite 

 or lithiophilite is the parent species. This is beyond all doubt 

 an original mineral in the vein, occurring intimately associated 

 with the albite, quartz and spodumene. With it, sometimes 

 entirely enclosed by it, we find another of the Branchville 

 species, triploidite, which seems to be also an original mineral. 



The masses of lithiophilite are as a rule unaltered, showing 

 only a little oxidation on the outer surfaces, and on the fracture 

 surfaces an occasional thin film of a bright blue crystallized 

 mineral in minute amount, resembling vivianite. In some few 

 cases they have a distinct though rough crystalline form, and 

 the planes 110, 120 and 021 have been identified; one of these 

 rough crystals is no less than eighteen inches in length and 

 weighs fifteen pounds. The angles measured are mere approx- 

 imations, but they are interesting as showing, as has been 

 assumed, that the form of lithiophilite is the same as that of 

 triphylite. We may add here that a small crystal found some 

 years ago resembles fig. 450 in Dana's System. 





Lithiophilite. 



Triphylite (Tschermak) 



110*110 = 



48° 



47° 



110 a 120 = 



17 -18° 



17 31' 



010^021 = 



42 



43 31 



The cleavage angle 110 /\ 110 was found to be 48° 30' to 49°. 

 Occasionally the masses of lithiophilite are extensively changed ; 

 this is true especially of some of the large nodular inclusions 

 in the vein. It is most interesting in these masses to note the 

 change from the perfectly fresh lithiophilite through a zone in 

 which the green chlorite-like dickinsonite is more or less dis- 

 tinctly represented to the hureaulite beyond. This change of 

 the lithiophilite into hureaulite can often be observed, and the 

 interpenetration of the two minerals is well shown under the 

 microscope in sections cut parallel to the basal cleavage. A 

 thin line of eosphorite often crosses the hureaulite. Some- 

 times with the dickinsonite we have also fairfieldite in clear 

 foliated masses, and reddingite in light pinkish crystals and 

 crystalline masses. It is impossible to lay down any general 

 rules in regard to the order of occurrence of these minerals or 

 their method of arrangement. On the contrary they occur 



