The most abundant rocks also contain huge amounts of potassium, but which is expensive to extract.
Neither in nature nor in agriculture potassium is ever a limiting nutrient like nitrogen and phosphorus.
For modern cultivated lands potassium must be indeed used as a fertilizer, because much of what exists in the soil is removed by remaining in the plant parts that are harvested then transported elsewhere. Another part of the potassium may be washed away by intensive irrigation.
So the potassium that is taken away depending on the cultivation methods that are used must be replenished. However its abundance is such that this will never be a problem.
And I even live in one of the blue states with lower P in the soil.
https://pubs.usgs.gov/sir/2017/5118/sir20175118_element.php?...
He also discovered commercial compost can be crap, since it hasn't broken down enough and soaks up nitrogen as it finishes its decomposition in the ground. So if your potatoes are struggling in something like that, slather on some urea and they'll perk (and green) right up.