What Gems Are Found in Minnesota?

Lake Superior Agate

• The state gem of Minnesota, Lake Superior agate is widely distributed across this part of America. The semi-precious gems were formed around 1.1 billion years ago, when a massive rift opened up in the center of what is now the U.S. and thousands of iron-rich lava flows came out of the earth. This particular type of agate was originally found around Lake Superior but came south in a massive lobe of glacial ice during the end of the last great ice age, around 15,000 years ago.

  Due to the oxidation of iron in its formation, Lake Superior Agate tends to be reddish, though it can be orange or yellow, and is attractive to collectors due to its striking banded patterns. Of particular value is the 'eye agate', which is a rare gem with perfectly-rounded bands on its surface.

Thomsonite

• The Thomsonite deposits found across the state of Minnesota were created from lava flows more than 600 million years ago. The lava seams trapped gases and created bubbles in the seams; these bubbles eventually were filled by minerals, leading to the formation of this relatively common gem. According to Thomsonite.com, the biggest deposits within the state can be found on the beaches between Tofte and Grand Marais, as well as on the Cook Lake County line; gem-like quality stones can be found on these beaches.

  While pure Thomsonite is bright white in color, the presence of other compounds, including those based around iron, leads to discoloring, with green, grey and blackish tints common. During the 1920s, '30s and '40s, the gem was commercially mined along the Lake Superior shoreline, though this practice soon became economically nonviable.

Binghamite

• Discovered by William Bingham in 1936, Binghamite is a quartz stone containing fibers of goethite, which is only found within the Cuyana iron range in Crow Wing County, Minnesota. As with the equally prized tigereye, the semi-precious gem features a chatoyant luster and, due to its being formed close to large deposits of iron ore, usually boasts a red, black or gold color. Binghamite is also known as silk stone, though only when a gem's patterning is arranged in straight, level lines.