Frequently Asked Questions (or FAQs)

What kind of rock is this?

There are three basic rock types—igneous, metamorphic, and sedimentary. All three rock types can be found in Minnesota. Igneous rocks form from molten liquid called magma. Metamorphic rocks form when pre-existing igneous or sedimentary rocks are subjected to intense heat and pressure, altering their original state. Sedimentary rocks are formed from the accumulated debris of weathered rock, or by chemical precipitation.

In general, undisturbed igneous and metamorphic rocks tend to be located in northern and western Minnesota, while undisturbed sedimentary rocks are found in the southeastern portion of the state. However, the majority of Minnesota’s bedrock is blanketed by unconsolidated glacial deposits that can contain all three rock types. The locality in which you found the rock sample can be very important in helping you determine the rock type.

Below are some of the common rocks found in Minnesota. You can find a more detailed description on our Common Minnesota Rocks page, as well as in Minnesota At-A-Glance: Common Minnesota Rocks.

Common rocks found in Minnesota:

Polished section of a gneiss sample.

Photo courtesy of Michael C. Rygel via Wikimedia Commons

Hand sample of greenstone (metabasalt).

Photo courtesy of James St. John / CC BY (https://creativecommons.org/licenses/by/2.0/)

Iron-formation/taconite

Banded iron formation (or BIF) from the Precambrian of Minnesota.

Photo courtesy of Amy Block

Graywacke sedimentary rock.

Photo courtesy of James St. John / CC BY (https://creativecommons.org/licenses/by/2.0/)

Granite from the Giants Range Batholith in the Precambrian of Minnesota.

Photo courtesy of James St. John / CC BY (https://creativecommons.org/licenses/by/2.0/)

Mica schist

Mica schist example from the Precambrian of New York.

Photo courtesy of James St. John / CC BY (https://creativecommons.org/licenses/by/2.0/)

Outcropping of Sioux Quartzite from the Precambrian of Rock County, Minnesota.

Photo courtesy of Mark A. Jirsa

Basalt lava flow from the Precambrian of Minnesota.

Photo courtesy of James St. John / CC BY (https://creativecommons.org/licenses/by/2.0/)

Layered gabbro of the troctolite series in the Duluth Complex of Minnesota.

Photo courtesy of James St. John / CC BY (https://creativecommons.org/licenses/by/2.0/)

Lake Superior agate.

Photo courtesy of Lech Darski / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0/)

Anorthosite

Anorthosite xenolith in the Precambrian of Minnesota.

Photo courtesy of James St. John / CC BY (https://creativecommons.org/licenses/by/2.0/)

Quartzose sandstone of the Upper Cambrian Jordan Sandstone, Stillwater, Minnesota.

Photo courtesy of James St. John / CC BY (https://creativecommons.org/licenses/by/2.0/)

Shale/mudstone

Outcropping of Ordovician Glenwood Shale in Minnesota.

Photo courtesy of Julia R. Steenberg

Limestone/Dolostone

Carbonate rock sample with fossils from the Ordovician of Minnesota.

Photo courtesy of Andrew J. Retzler

Glacial till

Till sample from a core drilled in Dodge County, Minnesota.

Photo courtesy of Katherine J. Marshall

What kind of fossil is this?

Fossils give us a glimpse of what life was like on Earth in ancient geologic time, as well as a window into past climatic conditions. A fossil is a trace or remains of an ancient animal or plant preserved within rocks or unconsolidated material. Fossil evidence of some of the most primitive life forms (i.e., algae and bacteria) can be found in the older Precambrian rocks of northern Minnesota, while more complex plant and animal fossils are preserved in the sedimentary rocks in the southeastern portion of the state. Much like determining the type of rock sample found, the locality and type of rock in which you found your fossil sample is very important for making a detailed identification of the specimen.

There are many online resources for helping one identify a particular fossil specimen in general, but more expertise is usually needed to properly identify the specific genus or species. For more detailed information about fossils found within Minnesota, you can visit our Fossils page or any number of the links below:

In general, the types of fossils found in Minnesota include the following:

It is also important to keep in mind the many inorganic (nonliving-sourced) structures one may come across that can be mistaken as fossils. These structures are known as pseudofossils, and can include:

Is this a meteorite?