tonsteinn.
/ˈtɒnstʌɪn/ Geology.
A rock composed mainly of kaolinite which is commonly found in association with certain coal seams, or a thin band of such a rock (see quots.).
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the world > the earth > structure of the earth > constituent materials > rock > metamorphic rock > [noun] > other metamorphics
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tonstein1961
greenlandite1981
1961 I. A. Williamson in Mining Mag. CIV. 9 Tonsteins are essentially argillaceous rocks containing kaolinite in a variety of forms together with occasional detrital and carbonaceous material.
1971 Nature 6 Aug. 371/2 The thin, curious, kaolinitic bands called tonsteins discovered more recently in the coalfields of Western Europe have provided welcome additional markers for coalfield correlation.
This entry has not yet been fully updated (first published 1986; most recently modified version published online June 2018).
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n.1961