>>38399642>what does geodude eat? he's just a fucking rock.Unironically rocks.
I had a look at the whole line: Geodude, Graveler, to Golem, and they only mention it very briefly, but they do in fact eat minerals n' so forth.
Geodude probably doesn't 'start' eating rocks, but instead start on soft soil, mud, clay, compost, and a mixture of organic and inorganic sediments or whatever to build up the proper gut flora and microbes they'll need when they get older. The 'dex says they roll DOWN the hills they live on to search for food, so they either can't eat the rocks around them, there's competition, or most likely both.
Graveler and Golem though seem to pace up and down the faces of mountains in search of rocks and minerals- with a particular pension for rocks covered in mosses or lichens. They'll reach the top of the hill and then roll down to start the 'grazing' process all over again.
Throughout their lives Geodude, Graveler, and Golem all compete for territory and resources, so the various rocks must have varying nutritional and mineral content that's important to them. The difference between why we, as Humans, can eat things like corn, but just plain ol' grass isn't very nutritious.