Minnesota shares its border with Lake Superior on the northeastern side and is famous of agates found here. Minnesota is has various types of rock with formations including metamorphic, igneous and sedimentary rocks. Some known minerals and gemstones that can be found in Minnesota are agate, binghamite and thomsonite. A variety of fossils are also present at various locations of the state.
Lake Superior Agate
Lake Superior agate was declared as the official state gemstone of Minnesota in 1969. The Lake Superior agates are also known as ‘lakers’ at times and occur in colors such as yellow, red, orange due the rich iron content. These agates were formed billions of years ago as a result from a volcanic eruption which caused molten lava rich in iron from deep below the earth to rise and flow. The lava trapped air bubbles and after the lava had cooled, underground water seeped into these bubbles along with many minerals and formed agates.
Due to the weathering of the volcanic rocks and glacial activity, these agates flowed down to various locations and are now found throughout the state of Minnesota at various river basins, gravel pits and gravel dumps.
The Lake Superior agates are generally small, however very large and heavy weight agates are also found in the state. The larger and rare variety of these agates can weigh up to twenty pounds.
There are different kinds of Lake Superior agates found in Minnesota. The agate known as the fortification agate which has unique patterns of sharp bands connected to each other are the most common ones found in Minnesota. The water level agate is another variety of the fortification agate in which parallel horizontal bands can been seen. A rare and precious variety of Lake Superior agate is the eye agate which has rounded bands on the surface that gives the appearance of an eye. The peeled agates, water washed agates and seemed agates are some more varieties of the Lake Superior agates found in the state.
The mineral thomsonite is a variety of zeolite. These minerals were formed at the same time as the Lake Superior agates as a result of the volcanic activity that took place billions of years ago along Lake Superior’s northern shoreline. Thomsonite occurs as rounded and banded structures with colors such as white, pink, beige, light brown, light yellow, light grey and light orange.
Some attractive and multicolored samples of thomsonite can be found at Thomsonite Beach located on the shores of Lake Superior in Cook County.
Binghamite is a rare variety of quartz which is composed of strands of hematite or goethite and occurs in places with rich iron content. Binghamite is found in colors such as gold, red, black, yellowish and sometimes is even multicolored.
The Cuyuna Iron range situated in Crow Wing County of Minnesota is the only location where binghamite has been found.
A large variety of fossils can be found at various location of Minnesota. Fossils of marine animals such as corals and fish as old as 380 million years that belonged to the Devonian era can be found at the north central region of Minnesota. This area also has fossils of oysters, snails, shark teeth and clams that belonged to the Cretaceous Period.
More than two million years old fossils of algae can be found at the Precambrian iron formation situated in the northeastern part of the state. Southeastern Minnesota is home to fossils of cephalopods and trilobites from the Ordovician era.