Rock Blocks beat the heat, make mama happy

Probably another adventure to file under "supposed to be for the kids, but mom ends up doing it anyway," but that's really OK. I just about love this idea.
Everyone has painted rocks. I myself have painted more rocks than most people, but it seems that every time I do it, I raise the bar. Of course, I can remember one of my earliest rock-painting experiences-- painting porous gravel with some white paint that I swear was wall primer.
But I loved 'em.
These, however, are much better, and make for a great activity, both while you make them and after you're done.
To make your own rock blocks, you need a pack of rocks. Sure you can collect them if you're lucky enough to live in an area of polished and smooth non-sedimentary rocks. Or, for a whopping $2, you can get a bag at a craft store. I suggest the craft store, because the rocks will be mostly similar in size and also conveniently located in the same place as the other materials you will need:
OUTDOOR paints
brushes

Then you just paint away, outside when it's pleasant, inside when it's a scorcher. These rocks took a few coats to make them so appealingly opaque, and once they are dry, feel free to decorate some, all, or none. Once dry, step back and smile because you've just created the perfect bridge between indoor and outdoor play. These babies are [supposed to be] waterproof, so leave them outside if you want! Or bring them in for a little substantial playtime.

Build with them: can you stack them 3 high? What about 4? A pyramid?
Game with them: copy this pattern? Look at this pile--close your eyes while i take one away-- what's missing?
Art with them: make a decorative center piece, line a trail around yard with the best-looking cairns you've ever seen
etc. etc. etc.

Mostly, enjoy the connection between inside, outside, nature, toy, math, and art. All in one beautiful pile of rocks.