Visited Minneapolis to see my younger son, and we went to a popular recreation spot in the city: Harriet Lake.  Adjacent and just north of the lake is a park with flower gardens.  In one of these gardens - Peace Garden - there were blocks of limestone and dolostone used as decorative borders.  Their size ranged from about the size of a bowling ball to a 5-gallon bucket, and some had vugs in them filled with botryoidal chalcedony with a variety of colors.  The only collecting I could do was by photograph.  When I got back home, I did a little online research and found that this is Prairie du Chien dolostone.  While I only saw chalcedony, this dolostone can also have vugs with quartz, calcite, and hematite.

Looks almost like a brain in some pictures.  Do you have any specimens after being soaked in acid?