Chickens use particles from the size of sand up to about the size of a pea as grit. How long it lasts before it is disposed of by passing on through their system depends on what size it was to start with and what material it was made of. Granite is a hard material and will last longer than other materials. Sandstone is fairly hard but it will break apart into the individual sand pieces pretty fast under pressure so it does not last real long. Limestone will work as grit but not real well. The chicken's digestive system produces acid, just like a human's, and the acid dissolves the limestone. They have to replenish it a lot. That's the reason oyster shell will not work as grit. Oyster shell is not as hard as limestone and the acid dissolves it too fast for oyster shell to do any good.
Chickens are very adaptable and can do well in a lot of different conditons and use a lot of different things. Chickens do seem to prefer the larger chunks for grit. They don't have to eat as much. But they can get by on the smaller stuff. They just eat it constantly. Play sand is already ground so smooth and is so fine that it will not work well at all. It will pass through their system too fast. Coarse sand, like construction sand, works much better. And even better is something with larger chunks in it. But they can do OK on the coarse construction sand.
I've kept chickens in a run with no grit provided. When I processed them, their gizzard had pretty much all sand since they had long since used the larger pebbles available. It was not unusual when they took a dust bath for them to peck at the dirt and eat that. They grew well and produced eggs well. When I put the bag of pea gravel in the run and let them free range, I noticed larger chunks in their gizzard. I did not notice any difference in their growth rate or egg production rate due to larger size of grit being available.
While I did find a plum pit in the gizzard of a 22 week old rooster, the largest size they normally use for grit is about the size of a pea. You do not want them eating tacks, small nails, or wire. Those can puncture the gizzard when they try to grind them up and cause a slow death. I've seen warnings about them eating glass but I am not absolutely convinced that eating glass is all that dangerous. Many rocks are also very hard and sharp, such as flint. It is still probably good practice for them to not eat glass though. Why tempt fate?
