286 



NEW YORK STATE MUSEUM 



of schistose appearance. To the unaided eye the rock appears 

 homogeneous, but when examined more carefully with the aid of 

 the microscope it is usually observed to contain more or less residual 

 tremolite that has not succumbed to the alteration process. The 

 conversion of tremolite to talc requires one molecule of water for 

 each tremolite molecule. It is, however, not simply a process of 

 hydration, since the tremolite contains about 13 per cent lime (CgO) 

 which is discharged from the combination and becomes free to 

 associate with any available acid radical. 



Foliated or crystal talc is present to a minor extent in most of 

 the occurrences in the Edwards district. It occurs in seams and 

 other openings, where it has been deposited doubtless by waters 

 circulating through the deposits, to which the conversion of tremolite 

 into the fibrous mineral is ascribed. That some of the talc should 

 be taken into solution and reprecipitated apart seems only natural. 

 In one mine (Balmat) the two varieties occur in contiguous layers, 

 the foliated talc forming a seam on the hanging wall, unmixed with 

 the fibrous mineral. 



Massive talc that has no definite structure or texture is the variety 

 found at Natural Bridge. It appears homogeneous and dense in 

 the specimen, but microscopically is an aggregate of minute grains 

 and scales whose precise character is not always apparent. The 

 product of this locality is probably a mixture of several minerals 

 of secondary nature, including serpentine, chlorite and kaolin, as 

 well as talc. Its derivation is uncertain, as no traces of the original 

 anhydrous minerals were to be seen in the many samples that have 

 been examined. . 



Analyses of New York talc 





I 



2 



3 



4 



5 



Si02 



60.59 

 •13 



} 



59-92 

 ■50 



62. 10 

 1.30 



2-15 



32.40 

 2.05 



68.9 

 1-3 



""'26.'6 

 . .8 



2.4 



{^ 



48.16 

 7-43 

 3-15 



AI2O3 



FeaOs 



FeO 



.21 

 1. 16 



34-72 



MnO 



.76 



31-37 



-57 



.48 



6.25 





MgO 



27.44 



.2S 



CaO 



NaoO 







HoO 



3-77 



13-74 





Total 



100.58 



99-85 



100,00 



100. 



100. 17 



I, 2 Fibrous talc, Edwards district, Dana's System of Mineralogy, p. 679. 



3 Fibrous talc, Edwards district, N. Y. State Mus. 49th Ann. Rep't, v. 2, p. 670. 



4 Fibrous talc, Talcville, Edwards district. Communicated by A. McLintock. 



5 Massive talc, Natural Bridge, R. W. Jones. 



