



C. H. Smyth, Jr. — Pseudomorphs from New York. 309 



Akt. XXXY. — Pseudomorphs from Northern New York ; 

 by C. H. Smyth, Je. 



Pyroxene after Wollastonite. 



While studying the mineral deposits of contact origin in 

 the town of Diana, Lewis County, the writer collected several 

 specimens which presented the appearance of pseudomorphs; 

 and such, upon further examination, they have proved to be. 



The surfaces of these specimens are rough and rounded, as 

 is so commonly the case with pseudomorphs, while fractures 

 show the crystals to lack homogeneity of structure, the mineral 

 of which they consist having a pronounced cleavage, which has 

 different directions in different parts of the crystal. The 

 specimens are pale greenish-gray, becoming colorless in thin 

 splinters and in sections. While the rough and curved faces 

 and rounded edges make it impossible to determine the origi- 

 nal form with absolute accuracy, the approximate measure- 

 ments afforded, together with the habit of the individuals and 

 of the aggregates, can hardly be explained except as inherited 

 from wollastonite, an abundant mineral of this locality. 



Thin sections show each crystal to be made up of a number 

 of individuals of monoclinic pyroxene, in irregularly bounded 

 plates, variously oriented with reference to each other and to 

 the external form derived from wollastonite. The pyroxene 

 shows the usual optical and pyrognostic characters, is colorless, 

 and free from inclusions other than calcite, which occurs as 

 rounded or sinuous patches in and between the plates of 

 pyroxene. This calcite seems to be an infiltration from the 

 surrounding limestone, rather than a product of the alteration 

 of the original wollastonite, though part may be of the latter 

 origin. 



In the hope of obtaining further evidence as to the nature 

 of the mineral replaced by pyroxene, a number of specimens 

 of Diana wollastonite have been examined, and, in several of 

 them, grains and strings of pyroxene have been found. While 

 these grains look rather like inclusions, it seems quite certain 

 that in reality they mark the initial stages of the process 

 which finds its completion in the specimens above described. 

 This is even more strongly indicated by thin sections in which 

 the pyroxene may be seen filling cleavage cracks and irregular 

 fissures and cavities in the wollastonite. 



The chemical changes involved in the alteration of wollas- 

 tonite into pyroxene are much simpler than in the case of scap- 

 olite and mica, described below. Yet, nevertheless, the former 

 alteration seems to be much less common. This is not surpris- 



