Lake Superior Agates are unique from other agates due to their strong red color. This comes from the oxidized iron introduced to them during their formation. Beginning as small bubbles of volcanic gasses in lava that hardened, ground water circulated silica along with the iron, which over time crystallized to form agate.
A massive glacier that moved across what is now Minnesota some 10-15,000 years ago, uprooting much of the agate formations and depositing them along the shores of Lake Superior. Between the smashing force of the glacier that dragged them and the gentile waves of the lake, Lake Superior Agates tend to be found in roughly polished rounded masses.
Lake Superior Agates are the state mineral of Minnesota, and are also found in the areas of Wisconsin, Michigan's Upper Peninsula, and Ontario that border the lake.