124 RE-EXAMINATION OF AMERICAN MINERALS. 



These correspond to the analysis of margarodite from St. 

 Etienne, in which Delesse found 



Si A-l Pe Mg Na K H Fl 



46.23 33.08 3.48 2.10 1.45 8.87 4.12 trace=99.33 



In a former paper we have mentioned the difficulty of ob- 

 taining a correct formula from the analyses of margarodite, 

 owing to slight differences in the protoxides. The relation 

 of the oxygen of the silica to that of peroxides in most of the 

 analyses is as 3 : 2. 



The specimens examined were received from Professor 

 Silliman, jr. 



18. The Chesterlite Talc— a Mica. 



Associated with the chesterlite a micaceous mineral is found, 

 which has been called talc. It occurs in implanted crystals, in 

 minute tuft-like aggregations on dolomite ; there is frequently 

 an iron stain upon the surface, due to the decomposition of some 

 of the minerals with which it is associated ; the crystals are 

 seldom over a line in diameter. Its chemical composition is 

 that of a mica; but owing to the small amount examined it is 

 impossible to say positively whether it be muscovite or mar- 

 garodite, although from its association we are inclined to 

 consider it muscovite. 



Silica 45.50 



Alumina 34.55 



Peroxide of iron trace 



Lime 2.31 



Magnesia 1.08 



Potash 8.10 



Soda 2.35 



Water and carbonic acid 5.40 



99.29 



A large portion of the lime and magnesia is doubtless due 



to the dolomite with which it is associated. The specimen was 



received from Mr. Thos. F. Seal. 



19. Ehodophyllite, identical with Ehodochrome. 



The violet-colored mineral which occurs at Texas, Pa., and 

 was circulated among mineralogists as "violet talc," has been 

 analyzed by Dr. G-enth,* of Philadelphia, who found for it a 



*Proc. Acad. Nat. Sci., Phil., vi, 122. 



