pumice stone
US /ˈpʌm.ɪs stoʊn/
UK /ˈpʌm.ɪs stoʊn/

1.
a very light, porous volcanic rock used as an abrasive, especially for scrubbing and polishing
:
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She used a pumice stone to smooth her rough heels.
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The artist used powdered pumice stone to create a textured surface on the canvas.