HI, Rick.
I have also started to add rock to my soil. I can buy compost from the green waste program for $20 a yard. I think I may have reached the point where I am actually adding too much compost. I have been adding the red lava rock for $65 a yard. It's 5/16" or 3/8" in size for the largest particles.
I grow bearded iris and also Louisiana iris in large raised beds that are lined with pond liner. The Louisiana beds are kept wet and I have no problem with cracking and shrinking of the soil. Not so with the bearded iris. But adding rock seems to help the problem. The soil is to the point where I am going to have to back off on the amount of compost I add. I have been thinking about adding sand to help break up the clay. Maybe I should look at bark instead?
