alum shale

noun

variants or alum slate or less commonly alum schist
: a shale or clay slate originally containing pyrite and after weathering containing aluminum sulfate formed by the action of sulfuric acid from the decomposition of the pyrite on the aluminous materials of the rock

Word History

First Known Use

1737, in the meaning defined above

Time Traveler
The first known use of alum shale was in 1737

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Dictionary Entries Near alum shale

alumroot

alum shale

alumstone

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Cite this Entry

“Alum shale.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/alum%20shale. Accessed 28 Nov. 2024.

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