I have been buying a 5lb bag of "chicken grit". It looks like smooth very white stones only it's not rock. They go through 5lbs fast, so I asked for a bigger bag. When I got home and opened it, it was crushed oyster shell and had sharp edges and some had very pointy ends. Can chickens eat this? If I tried to swallow some, it would be like razor blades. Thanks for any advice.