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XXIlOw Asbestus, Chlorite, and Talc. By THOMAS THOMSON, 

 M. D., F.R.SS.L. & E. &c., Regius Professor of Chemistry in 

 the University of Glasgow. 



(Read 16th February 



.NOTWITHSTANDING the great progress which Mineralogy has 

 made of late years, towards the division of minerals into accu- 

 rate and well denned species, there are several groups which 

 occur in the oldest mineral systems extant, and which have con- 

 tinued to the present time with very little alteration or improve- 

 ment. I allude to the minerals classed under the names of As- 

 bestus, Chlorite, and Talc. As these minerals, with the excep- 

 tion of certain varieties of talc, have never been observed in 

 crystals, the important labours of the crystallographer have not 

 been able to throw any light upon them. But, as all mineral 

 species are chemical compounds, and as each species consists of 

 the same constituents united in the same proportions, I thought 

 it not unlikely that an accurate chemical analysis of the different 

 varieties of minerals, at present classed under the names Asbes- 

 tus, Chlorite, and Talc, would be likely to throw considerable 

 light on their nature, and would inform us whether they consti- 

 tute peculiar mineral species, or are only varieties of species 

 already well defined and characterized. I propose, in this paper, 

 to give an account of the result of this investigation. 



