Sentence:  Argiento had been trained so rigorously by the Jesuits that Michelangelo was unable to change his habits : up before dawn to scrub the floors , whether they were dirty or not ; water boiling on the fire for washing laundry every day , the pots scoured with river <WSD>sand</WSD> after each meal . 
Meaning of the word marked with <WSD> tags:  a loose material consisting of grains of rock or coral