I have gravelly soil and let them free range an hour before sunset daily weather permitting.
But I still have Poultry Grit available. .I'm still on my first 25# bag over 2 years for 5 hens most of that time. I feel better to have it available. It's $8.99 for 25# at TSC. You can also get a 5# bag...
If you give them scratch grains or mixed bird seeds as a treat scattered on the ground. Mix in 1 pound of Granite Grit to 40 pounds of Scratch.
Or just scatter some in coop or pen, wherever they scratch.
If you don't give Scratch or seeds. You can mix in 1# to 40# of feed. They won't eat it all...