I'd say the coloration is pretty spot-on with the usual Iowa diorite/granite or gabbro... But your states DNR lists basalt as extremely common... So perhaps that is also a possibility.
Although diorite was commonly used for stone tools, your example appears to be a typical water/glacial worn cobble. No defined utilization wear to any one area, simply smoothed in general.
Thanks for sharing it!
~Tejaas~