Graton and Schaller — Purpurite, a new Mineral. 147 



veinlets, and appears to have been deposited from solution in 

 cavities. Occasionally, however, it is found in the midst of the 

 pegmatite as if it were an original mineral. 



The question of the origin of purpurite is one of interest. 

 Pegmatite dikes believed to be closely related to the tin-bear- 

 ing dikes carry the rare-earth phosphate, monazite. Among 

 the primary minerals of the tin-bearing pegmatites are cassi- 

 terite, tourmaline, apatite, spodumene, lepidolite, and a yellowish 

 brown, iithia-bearing phosphate which is doubtless lithiophilite. 

 The last two minerals have been found only in small quantities. 

 Partially decomposed specimens of this pegmatite frequently 

 show much manganese dioxide as thin mammillary coating on 

 the other minerals. Ilmenite is often included in crystals of 

 cassiterite. It is evident, therefore, that the elements manganese 

 and iron (as monoxides), lithium, and phosphorus (as phosphate) 

 were primary components of the pegmatite magma. 



The mineral presumed to be lithiophilite is always surrounded 

 by a coating of black, secondary material. In one case, a nar- 

 row zone of purpurite was found between the lithiophilite and 

 the black mineral. It is believed that this single occurrence 

 furnishes the explanation of the origin of purpurite. A lithia- 

 manganous-ferrous phosphate, probably lithiophilite, was 

 attacked by oxidizing solutions. The lithia was almost wholly 

 carried away, while of the remaining elements, iron and man- 

 ganese were oxidized to the state of sesquioxides and were 

 recrystallized with the phosphoric acid and water to form 

 purpurite. The trace of lithium which this mineral contains 

 is a remnant of that from the lithiophilite. In some cases the 

 recrystallization took place without transportation of the 

 materials, forming pseudomorphous replacements, but in gen- 

 eral the materials were carried in solution to cavities and there 

 deposited. 



Purpurite is probably orthorhombic, but no specimens have 

 been found which show crystal outline. A cleavage which is 

 probably pinacoidal is of rather perfect development, but the 

 cleavage surfaces are often curved as if the orientation of 

 adjoining grains were not exactly the same. A second cleav- 

 age, presumably at right angles, is considerably less distinct. 

 The mineral has an uneven fracture and is rather brittle. It 

 is scratched without difficulty by the knife, but on the other 

 hand just scratches fluorite, and hence has a hardness of 4-4*5. 

 Mr. Schaller determined the specific gravity as approximately 

 3 # 15. In color the mineral is a rich deep red or reddish pur- 

 ple, sometimes with a slight bronzy iridescence, and not 

 uncommonly darker on the cleavage planes. The powder and 

 the streak have a decided purple or deep rose color. The 

 mineral has a peculiar satiny luster or sheen, more noticeable 

 on fracture surfaces than on cleavage planes. 



