MINERALOGY AND CHEMISTRY OF TONSTEINS FROM CARBONIFEROUS SEQUENCES IN GREAT BRITAIN

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Abstract
SUMMARY: Tonsteins from Westphalian Coal Measures in England are compared mineralogically and chemically with tonsteins of volcanic origin from coalbearing sequences of Namurian and Westphalian age in Scotland. Differences are apparent between tonsteins occurring as partings within coals (“coal tonsteins”) and those interbedded with inter‐seam sedimentary rocks (“non‐coal tonsteins”). The coal tonsteins show higher titanium values and in some cases contain minerals of the goyazite series. Sedimentological, mineralogical and chemical evidence is reviewed and the conclusion reached that all tonsteins examined could have originated as thin layers of volcanic ash. Subsequent alteration depended upon the environment of deposition into which the ash fell.