Types of Rocks Found In Illinois: 11 Common Collectible Rocks and Fossils You Can Find

The great and bustling city of Chicago overshadows the rest of the state of Illinois.

In the minds of many people, the state itself exists as a kind of appendage to the city.

But there is much more to the Prairie State than its most famous city.

Illinois is one of the most geologically interesting regions in the country.

Types Of Rocks Found in Illinois (A Guide)

Although Illinois is relatively flat now, it was not always so.

Boulders and gravel brought in by glaciers hundreds of thousands of years ago lay under the surface of the land.

This has led to huge coal deposits, which are mined throughout Illinois.

At shallower layers, one can fine interesting rocks and fossils.

Any collector would be pleased by the types of rocks found in Illinois.

Here are some of the rocks found in Illinois:

1. Agate

This rock often has a streak of white, which is one of its most distinguishing features.

Agate is a microcrystalline form of quartz.

It has a colorful appearance, and is found in many regions throughout the world.

Some forms of agate have lace-like banding, which includes eyes, swirls, and other patterns.

Agate has a hardness of 7, and it has a wide range of practical applications.

It has been used to create precision pendulums, mortars, knife-beating edges for balances used in scientific labs.

You might enjoy this related article: Agate vs Onyx: What’s The Difference?

2. Pyrite

Pyrite has a brass-yellow sheen. It derives its nickname “Fool’s Gold” from its similarity to actual gold.

Prospectors once mistook Pyrite for the real thing.

Rock collectors who spot it can avoid such embarrassment by noting the differences between the two substances.

Pyrite differs from real gold by its hardness, brittleness, and crystal form.

The greenish-black streak also sets it apart.

Gold is all yellow, and when tested on a streak plate leaves a yellow streak.

You might also enjoy: Is Pyrite Magnetic? (Plus Other Pyrite Facts)

3. Fluorite

This is a very popular mineral.

It comes in the form of colorful crystals.

Pure fluorite is colorless.

However, its impurities can yield a wide spectrum of colors, some of which can be quite stunning.

Fluorite has a wide variety of uses.

It is sometime sold in bulk, and used to light up living things in fluorescence under ultraviolet light.

It is also used in the production of hydrochloric acid and ceramics.

Some heavy industry companies also use it as a flux for removing impurities in metal production.

Fluorite is also used as a gemstone.

Its low hardness makes it malleable enough to be shaped be fitted into jewelry of all kinds.

You might also like: Fluorite vs Fluoride: Are They The Same?

4. Basalt

This is one of the most common and widely distributed type of volcanic rock.

It is composed of pyroxene, feldspar, magnetite, and biotite.

Basalt is distinguished by its dark-greenish color.

The minerals in the rock are fined grained and closely packed together.

You might also like: Silly Question, But Is Basalt Salty?

5. Geodes

The glaciers brought geodes to Illinois. They are a treasure for any rock collector.

These spherically shaped rocks are filled with layers of minerals and lined with crystals.

They are composed of chalcedony, and form a crystalline silica.

Quartz is the most common mineral in geodes.

And as nearly everyone knows, this mineral has a range of applications in industrial and consumer products.

Quartz is used in everything from laser technology to the jewel industry.

Geodes come in a wide range of sizes.

You can find rocks that are less than an inch thick and those that are more than a foot in length.

Fossils Found in Illinois

Here are some of the fossils found in Illinois:

1. Blastoid

These fossils are sometimes called sea buds.

It is known that blastoids had long hair-like brachioles which they used to sweep food into their mouths.

The latter was at the top of their body, and it was surrounded by small round holes that pushed food in and wastes out.

The oldest blastoid ever found in Illinois lived more than 420 million years ago.

This species survived until about more than 250 million years ago, and then became extinct.

One way of identifying a blastoid is through its general appearance.

Blastoids resemble small hickory nuts.

They are commonly found in river cliffs.

You might also find blastoids in stream banks of western and southwestern Illinois, especially in Randolph Country in the vicinity of the Ohio River.

2. Bryozoans

These tiny ancient animals grow in a variety of shapes and patterns.

They are mound-shaped, tree-shaped, and screw-shaped.

The skeleton has many tiny holes, each of which is the home of tiny animal.

What we know is that they spent most of their time on the sea floor.

The Bryozoans are some of the most common fossils in existence.

The oldest specimens are over 500 million years old.

Most fossils are found in shales or limestone beds through the state.

3. Cephalopods

These are the were the most advanced animals without backbones.

They had a highly developed nervous system and eyes that were very much like those of humans.

The mouth of this ancient animal was surrounded by long tentacles that were used as suckers.

The animal also had a tube through which it could force water and move about by jet propulsion.

Descendants of ancient cephalopods love on today in the South Pacific.

Most of the fossil forms of cephalopods have a calcareous outer shell.

The species lived nearly 460 million years ago.

And it is believed that some of them grew to be as long as 19 feet.

Many types of cephalopods are found in rocks in both Pennsylvania and Illinois.

4. Conodonts

These are small calcium phosphate fossils that are barely visible to the naked eye.

They can be found in various places in Illinois.

Many of these fossils have been shaped by erosion and continental glaciers.

Conodonts are useful to geologists because they help them correlate the age of rock formation from region to region.

5. Corals

These marine fossils look a great deal like flowers.

When they were living creatures, they had a stony external skeleton that connected their insides with radial partitions that divided the body into chambers.

Some corals lived in colonies composed of hundreds of individuals attached to one another by outer skeletal walls.

In some regions, they formed coral reefs that were hundreds of miles long.

Fossilized forms of coral are most commonly found in limestone.

Here, they sometimes make up a large part of the rock.

Fossil coral is also found in shale and sandstone.

6. Crinoids

Though often referred to as sea lilies, Crinoids are animals rather than plants.

They have a bony skeleton, and when they lived, they were held to the sea floor by a stony anchor.

The mouth, which was located on the top of their bodies, was used to sweep food into it.

Crinoid steam are common throughout the state of Illinois.

Many of the state’s limestone beds are composed almost entirely of crinoid plates and discs.

In Summary

If you are a seeker and collector of rocks and fossils, there is no better place than Illinois to hunt your treasure.

As can be seen, the state is filled with specimens that you can add to your collection.

Chicago is not the only draw.

The fields and plains of the larger state contain a trove of objects that you may not find elsewhere.