Graton and Schaller — Purpurite, a new Mineral. 151 



The amount of water given off at 105° is 3'31 per cent. As 

 all of the water is so readily given off, it is most probably pre- 

 sent as water of crystallization. 



Considering that the calcium and soda require some phos- 

 phoric acid, the ratio of W'fi^ : P 2 5 : H 2 is approximately 

 3:3:3. Combining the ratio of the calcium and sodium with 

 that of the iron and manganese, and reducing these to their 

 hydrogen equivalent, the ratio becomes 



BL ■ P_C> 4 + 3-04HO 



18-58 6-94 26-64 



or 2[H., 9 ,P.„0, M ] +-92H s O. 



The acid is therefore H 3 P0 4 The formula for the mineral 

 then becomes K'^O, . P 2 5 + H 2 0. 



It is not known in just what state of combination the cal- 

 cium and sodium are. They most probably represent some 

 slight impurity. If the manganic and ferric oxides are iso- 

 morphous in the sense that manganous and ferrous oxides are, 

 the ratio of Mn 2 3 to Fe 2 3 being nearly 2 : 1 is of no signifi- 

 cance and the formula then should not be written Fe 2 3 . 

 2Mn 2 3 . 3P 2 5 + 3H 2 0, but (Mn //7 , Fe ,,, ) a O,. P a O B +H a O, the 

 mineral purpurite being near the manganic end of an isomorph- 

 ous series having as its two end members : 



Fe.O t ..P,0, + H,O 



Mn,0,:P,0. + H,0. 



There are only a few hydrous phosphates of the normal 

 division in which the base is trivalent, such as scorodite and 

 strengite. All of these, however, contain more water than the 

 mineral here described. 



While no manganic phosphates were noted in the literature, 

 there are a number of arsenates containing Mn 2 3 , with none 

 of which, however, can purpurite be classed. Synadelphite, 

 ninkite, arseniopleite, and perhaps hematolite, contain Mn 2 3 

 with A1 2 3 or Fe 2 3 , while in durangite and arseniosiderite, 

 Mn 2 3 is reported in small amounts. 



The mineral fuses easily and readily gives off water in a 

 closed tube becoming yellowish brown. It is readily soluble to 

 a clear solution in hydrochloric acid, while in nitric acid a 

 black oxide of manganese separates out. The specific gravity 

 determined on the powdered mineral by the Thoulet solution 

 is approximately 3*15. 



