No, it's not ground corn husks. I have Chicken Grit, which is ground granite the size of small gravel...and I think Chick Grit is the same thing, just ground even finer. When mine were little like yours I gave them grit for Parakeets or Cockatiels (I bought it at Walmart in the pet aisle). It looked like sand with some tiny little rocks in it.
I think if you're giving them raisins and broccoli, you need to get some grit.
I think if you're giving them raisins and broccoli, you need to get some grit.