"To see a World in a Grain of ... / And a Heaven in a Wild Flower" (Blake) (4)

I believe the answer is:

sand

(Other definitions for sand that I've seen before include "Rub down (for painting)" , "Smooth down (surface)" , "George -, nineteenth century French novelist" , "Content of hourglass" , "Grit; powdered rock" .)

I've seen this clue in The Irish Times.

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