Genth.j ^"U [July is, 



phyllite of an almost silver-white color, and of silky lustre* The thickest 

 seams of the fibrous pyrophyllite, which I have seen, were 9 mm in thick- 

 ness, separated in the middle by a layer of pyrite. 



The purest specimens have a white to yellowish-white color, and a lustre 

 between silky and pearly, the latter especially visible when magnified ; the 

 fibrous particles show a somewhat laminated structure. Very soft. Spec. 

 Gr. = 2.804. 



Infusible, but strongly exfoliating when heated, leaving a mass of snow- 

 white silky fibres. 



Not decomposed by sulphuric nor hydrofluoric acids, nor by a mixture 

 of both. 



The analysis made with perfectly pure material gave the composition of 

 pyrophyllite, corresponding to the formula : Al 2 Si 4 O u + H 2 0. 



Silicic Acid 



Alumina 



Ferric Oxide 



Magnesia 



Water 



99.93 100.00 



This occurrence of pyrophyllite in coal slates and as the petrifying ma- 

 terial of coal plants is exceedingly interesting, and I believe it to be the 

 first time that it has thus been observed. 



Prof. Gumpel noticed that a mineral resembling pyrophyllite constitutes 

 the mass of many graptolites, but Prof, von Kobell has shown, by analysis 

 of specimens from Nordhalben, near Steben in Upper Franconia, that this 

 substance is not pyrophyllite, but a micaceous mineral, containing over 3% 

 of potassium oxide, which he called " gumpelite. " 



The petrifying material of coal plants in the Tarantaise in Savoy has 

 also been confounded with pyrophyllite, but we are now indebted to Prof. 

 Gumpel for an investigation of this subject.f His analysis gave 6.803% of 

 potassium oxide and 2.208% of sodium oxide. He has also made an analysis 

 of the mineral of tlie graptolites from Graefenthal, in Thuringia, which 

 gave 5.06% of oxides of potassium and sodium. 



All these analyses show that the substances found as petrifying materials 

 of coal plants in the Tarantaise and of graptolites are not pyrophyllite, but 

 varieties, or perhaps mixtures, of micaceous minerals of greater or less 

 purity, belonging to that group, which Prof. Dana puts under the head of 

 pinite, and which are so frequently met with in nature as the results of 

 alteration of numerous minerals, such as iolite, ncphelite, scapolite, feld- 

 spars, staurolite, cyanite, corundum, topaz, &c, &c, which, when pure, 

 would be recognized as damourite, paragonite, &c. 



University of Pennsylvania, July 14, 1879. 



* I could not get enough of it in a pure state for an analysis, but a partial 

 analysis proved it to be pyrophyllite. 

 t<i. Tschcrmnk, Mlneralogische and Petrographische Mittheilnngen IT, 2, 189. 



