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They'll peck at it and arrange it to their liking as they're dustbathing in it, but sand is far too fine to serve as grit. You will still want to provide standard granite grit for poultry to your chickens.
I have found that if you get the coarse sand it serves as grit, I have not bought grit in over a year and have not had a soft shell egg.
* not telling any one to not buy grit, this is just my choice *
Grit and calcium supplements (usually crushed oyster shell) are two different things that are often confused. Grit is what a chicken uses in its gizzard to help it grind up the food that's too tough or hard shelled to be digested by the acids in its glandular stomach. The best kind of grit is granite because it's rough and irregularly shaped. Sand, even coarse sand, is much too small to serve in this digestive function. Grit has nothing to do with egg shell formation, but everything to do with digestion. When chickens free range they often can pick up grit in the form of stones on their own, and sometimes even in a dirt run they'll be able to find enough stones. Of course, if all they are eating is chicken feed, the need for gritl is minimized.
Crushed oyster shell is a calcium supplement often provided free choice so that a hen needing a bit of extra calcium can select what she needs. Laying rations already contain calcium, so not every hen will need supplementation for proper eggshell formation.