Any rock can be painted. Some are more porous and may require a thicker paint for colors to be bright. I find rocks at the beach or other places in nature. Basic, acrylic paint works really well. You will probably want to start with a rock that is palm sized or smaller and one that has a fairly flat surface. Then, just go to town. Here is what I came up with:
After the rocks are painted, you can use them as paperweights, put them in your garden, or just display them in your home,
Enjoy,
Lī'ula