My two three year old DTs are also obsessed with eating rocks or anything white or shiny. This includes dirt, perlite, styrofoam that falls out of potted plants (mixed with the potting soil) gum wrappers, a spoon I use to dig in the garden, bird droppings- virtually anything they shouldn't be eating is a magnet. Especially anything white. They will spend ten minutes trying to eat a white spot off the brick walkway.
It was suggested to me to give them a cuttlebone to chew on, and they immediately took small bites of that, but continue to go after other things too. Last night Koko tried and rejected a June bug. He has previously eaten and enjoyed sowbugs, though...
It's disappointing that they have a wonderful garden full of tasty plants and grasses, but they'll go out and push the plants aside and chow down on dirt. I really have to watch what's on the ground- they'll eat anything.
Nanci

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*****
0.0.1 Classic Corn, 0.0.1 Cali King, 0.1 Nelson's Milk
1.0 Tricolor Hog, 0.0.1 Eastern Hog, 1.0 Florida King
1.0 Eastern Box Turtle, 1.0 Florida Box Turtle
0.0.2 Desert Torts, 2.0 Feral Pigeons