Geology of Missouri

Missouri is located on the North American Craton. The NA Cration is an ancient geologic struction. It makes up the core basement rock forming the North American continent.

Above the basement rock, making up the core of all continents, you can find bedrock. Bedrock is a dense, hard rock which in Missouri tends to be close to the surface. You can find igneous, metamorphic, and sedimentary rocks in Missouri that make up the basement and bedrock.

Metamorphic rocks are rate in Missouri, usually found only in the basement rock. Sedimentary rocks such as limestone are very common. They are formed by a very long process of erosion and compression.

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Mozarkite

Mozarkite is the official state rock of Missouri. It was designated as such in 1967.

Mozarkite is a type of chert. Chert is a hard, opaque rock composed of silica and generally occurs as nodules. Mozarkite is typically red, pink, or purple in color and has stunning bands or a mottled pattern. It is a favorite of lapidaries due to its unique coloring and ability to take a high polish.

Calcite

Calcite is the principal mineral in one of Missouri’s most common rocks, Limestone. Calcite is also found commonly in ore deposits, as a cementing medium in sandstone, or in small quantities in igneous rocks.

These Calcite crystals come in a variety of sizes. Calcite can be microscopic or grow to several feet in length. It’s quite common to see excellent examples of calcite in “dogtooth” shaped crystals. These crystals have a pyramid shape. Calcite does not vary much in color. It is generally white or a pale amber.

Some of the finest specimens of calcite are found in the lead-zinc mines in southern Missouri.

galena mineral sample

Galena

Streak: Lead-gray

Hardness: 2.5

Chemical Formula: PbS

Galena is the natural mineral form of Lead Sulfide, the most important ore of lead and silver. Galena is one of the most abundant sulfide minerals, a group which contains other popular minerals such as pyrite and cinnabar.

When fresh or tested on a streak plate, galena is opaque and a bright metallic gray. Galena can be found as a cubic, octahedral, or dodecahedral crystalline structure or a combination of these.

Galena deposits are found worldwide with notable deposits in the Lead Belt in the United States, the Sullivan Mine of British Columbia, and in the Driftless Area of Illinois, Iowa, and Wisconsin.

There is historically evidence to support the use of galena as far back as 6500 BCE as lead beads. Galena was also used in Ancient Egypt in cosmetic eye kohl.

Galena is often mined in the Bootheel area of Missouri located in the Southeast. The Southeast Missouri Lead District is the world’s most productive lead mining region.

Galena was once often found in and near Joplin, Missouri. These once productive mines are now closed and it is very difficult to find specimens in this area now.

Due to its importance in Missouri’s economy and development, Galena was designated as the official state mineral of Missouri in 1967.

Barite

Barite is a heavy non-metallic mineral. It generally comes in white, gray, or blue-gray coloring. Historically, Missouri has been a large Barite producer. Barite has been used in the past as a paint pigment, a source of barium for chemicals, and as a filler in rubber, textiles, and plastics.

The most common specimens of Barite that you may see for sale are bladed and opaque. These can be found in Washington County, near Potosi and Old Mines. Smaller crystals have also been found in Morgan and Moniteau Counties.

Photo: Baryte, Calcite by Robert M. Lavinsky This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.

Keokuk Geodes

Keokuk geodes are found in the north-eastern most corner of Missouri. They can also be found in Iowa and Illinois. These geodes get their name from the Iowa city of Keokuk, located at the center of the collecting area.

These geodes can be found easily in this area where they often wind up in stream channels where water has eroded the rock.

In a Keokuk geode, you can usually find beautiful white quartz crystals. The outer wall of these geodes is made up of chalcedony. When you find a keokuk geode it is not uncommon to find other minerals inside your geode. Pyrite, dolomite, and kaolinite have all been found inside keokuk geodes.

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    Sheffler Rock Shop

What Else Can I Find?

Of Course, these rocks and minerals aren’t all you can find in this great state. Things like coal, granite, limestone, and sandstone can be found throughout the state.

Sedementary Rock

Bituminous Coal is the most common type of coal to find in Missouri

Coal is a sedimentary rock that will burn. It is formed by compaction of decomposed fossils. Coal is black and often has a glossy luster. In Missouri, you’ll most likely find bituminous coal which occurs in horizontal seams in the Northern and Western parts of the state. When you find coal in Missouri, you can also commonly see impurities such as calcite, pyrite, and gypsum.

Limestone Quarry
Limestone Quarries are a common sight in Missouri

Limestone is another sedimentary rock often found in Missouri. It’s composed mostly of calcium carbonate, or calcite. It’s incredibly common to find the fossils of marine animals in Missouri limestone. Because of the frequency of limestone in most of the state, it contributes a fairly large amount to Missouri’s economy. This stone is used in a huge number of industries. Limestone can be crushed for agricultural lime, also known as Lime Sand, used for gravel roads, in concrete aggregate, and as building stone.

Sandstone is an interesting sedimentary rock composed usually of small particles of quartz. These small grains are held together with silica, clay, iron oxides, and calcite. This stone sparkles wonderfully in the sun due to the crystal faces of the grains. The materials holding the crystals together are often softer than the particles they hold and generally break easily. This means that the sandstone can be scratched or crushed easily. Sandstone can be used in building as stone or aggregate and glass manufacturing. Historically, sandstone was also used to make grinding stones used in mills.

Igneous Rock

Granite can be found in the Southeastern “Bootheel” part of Missouri. These higher quality granites have been used historically for building purposes as well as smaller pieces being used for riprap, gravel, and paving blocks.

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Author: Celeste

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