Much of Minnesota's nearly 87,000 square miles borders or includes water. The northeastern part of the state lies along Lake Superior, while the state includes a phenomenal 11,842 distinct lakes. Minnesota's sheer size and boisterous geological history contribute to the abundance of gemstones found there.
Lake Superior Agate
The official state gemstone since 1969, Lake Superior agates are banded quartz stones. Owing to the high iron content of the soil in which they are found, their predominant colors are red, yellow and orange. Ranging from pea-sized to over 20 pounds, Lake Superior agates are found in the northeastern and north-central part of the state.
As with Lake Superior Agate, Thomsonite owes its existence to long-ago lava flows along the northern shore of Lake Superior. Thomsonite is classified as a zeolite, meaning that it belongs to silicates and usually arises from volcanic activity. It is often formed in rounded, concentric bands that can be polished into individual rocks.
Minnesota is home to a number of jaspers, which originate in the state's iron ranges. One of these, Binghamite, is found in the Cuyuna Iron Range. It is multicolored yellowish to reddish. It demonstrates "chatoyancy," a property characterized by a concentrated band of light reflected across the center of the gemstone.