Do you have a link to the product?I checked the package of the grit I purchased a little closer and it says it is suitable for chicken, quail, bantam quail and finches. It does have several sizes.
I'm curious what it is.
I've purchased granite grit in bulk from the feed mill and sifted it all thru a 1/16" colander to get the smaller sized grit for the chicks.
I usually dig up a small piece of sod near the chicken run and sprinkle it with grit in the brooder at about 1-2 weeks old.