My garden contains many rocks 2 inches and more which have never stopped the roots. In a container though they would occupy a lot of space that would be better used for growing media. Al

If it were me, I would screen out the dust and the larger particles, and use pieces approx. 1/8" to 1/4" in size... size of particulate within a medium should ideally be as comparable as you can get them for the medium to work properly within a container environment.

That said, roots grow around whatever obstacle they come across, so that wouldn't be an issue... I would be more worried about creating a perched water table within the pot... or having the dust and tiny pieces fill in around the larger chunks, defeating the entire purpose of mixing your own medium.

I would also add another ingredient, such as coarse perlite. It's reasonably priced, easy to manage because it's light in weight, and most larger garden centers would carry it... or be able to order it for you. Another alternative would be small gravel pieces, like cherry stone or granite chips, pumice, or small lava pieces.

Anything up to 3/8" or so is ideal.