148 Graton and Schaller — Purpurite, a new Mineral. 



Although transparent in very thin pieces, the ordinary thin 

 section allows the passage of very little light through purpurite. 

 The colors in transmitted light are very beautiful. Pleochro- 

 ism is noticeable. Parallel to the cleavage the color is a deep 

 scarlet, inclining to rose-red, while across the cleavage the 

 absorption is greater and the color becomes a beautiful purple. 

 This absorption, it will be noticed, is similar to that of tourma- 

 line and a few other minerals, in which the greatest absorption 

 is at right angles to the direction of cleavage or elongation. 

 Extinction is generally parallel ; an inclination up to three or 

 four degrees, which has been observed in a few instances, has 

 probably been due to the orientation of the sections examined. 

 It may be, however, that the mineral is monoclinic, with a 

 very small extinction angle. Sections which were transparent 

 were not of sufficient size to give an interference figure. No 

 sections showing the intersecting cleavages were seen, and in 

 all the sections examined the traces of the cleavages are parallel 

 to the direction of greater elasticity of the section ; so if the 

 mineral is biaxial, the intersection of the cleavages is parallel 

 to a. This is also the direction of least absorption. The 

 refractive index is somewhat greater than that of Canada bal- 

 sam and probably lies between 1*60 and 1*65. The difference 

 of the indices or the double refraction is high, and although it 

 could not be measured at all accurately, is probably not much 

 below '060. One effect of this high double refraction on the 

 very thin sections examined is that under crossed nicols the 

 mineral appears to transmit as much and as brilliant light as 

 without polarization. The red interference colors are very 

 striking. 



The purple mineral is always covered or surrounded by a 

 greater or less thickness of a black or brownish black material 

 of pitchy luster and uneven or sub-conchoid al fracture. This 

 material, which is soluble in hydrochloric acid, has been found 

 by Mr. Schaller to contain iron, manganese, phosphoric acid, 

 and water. Under a lens the black material can be seen to 

 encroach upon the purpurite, eating in along the cleavage 

 planes and gradually replacing the purple mineral. It is 

 undoubtedly a decomposition product of purpurite and is cer- 

 tainly the same as that which surrounds the supposed lithiophi- 

 lite. Yiewed with the aid of the microscope it appears to be 

 a definite mineral, having an imperfect cleavage, and a brown- 

 ish yellow color in transmitted light. Extinction is nearly or 

 quite parallel to the cleavage, and the trace of the cleavage is 

 the direction of least refractive index of the sections examined. 

 Pleochroism is distinct and, as in the case with purpurite, 

 absorption is greatest across the cleavage. The index of refrac- 

 tion is greater than that of Canada balsam, and the double refrac- 



