245 



which condenses in the upper part of the tube. A higher tem- 

 perature causes the mineral to give out more water, and this water 

 was observed to restore the blue color to reddened litmus paper, 

 showing that it was slightly alkaline, probably from absorbed 

 carbonate of ammonia. By heating the mineral on paper cards 

 and on plates of lead the temperature at which exfoliation takes 

 place was ascertained to be between 500° and 600° F. By 

 the researches of Mr. Crossley it was ascertained that this min- 

 eral could be entirely decomposed by the action of a mixture of 

 sulphuric and chlorohydric acids; hence it was unnecessary to 

 attack it by fusion with fixed alkalies. The results of his 

 analysis are as follows : — 



99.92 

 Hence the approximative formula will be 



2 Al Si + 4 Mg Si + 3 Aq, 



which is the formula of Pyrosklerite, according to Kobell. Du- 

 frenoy, Traite de Mineralogie, T. iii. p. 503. While writing this 

 I have received a letter from Mr. J. D. Dana, who suggests that 

 the formula 



2Mg3 (Si Al)2 + 9H 



will answer to Mr. Crossley's analysis. 



The name Vermiculite having been given to this mineral in 

 1824 will take precedence over that of Pyrosklerite if the two 

 minerals should be regarded as identical. 



Mr. Teschemacher read a paper on the mineral which 

 had just been exhibited by Dr. Jackson. He referred to an 

 opinion expressed to the Society some years since, that 

 Vermiculite and Pyrophyllite of Hermann are identical. 

 He proceeded to compare Mr. Crossley's analysis of Ver- 

 miculite with Chonikrite, Pyrosklerite, Kammererite, Rho- 



