Indiana has an assortment of rocks specific to the area.
Here are 7 of the most common rock and mineral aggregates that you will find within this Midwest state.
Types of Rocks in Indiana (EXPLAINED)
Sandstone is a very porous sedimentary rock.
It has withstood the harsh weathering process of the earth’s surface to make sandstone a resistant mineral of quartz, feldspar, and rock fragments.
This rock varies in color, depending on the mixture of minerals.
Feldspar can leave brown, pink, gray, gold, or cream tones of color or leave bands of color throughout the stone.
The same holds true with different degrees of quartz.
This hard rock can be found all across Indiana.
Popular areas are in the Northwest part of the state where glaciers moved down from Michigan about 700,000 years ago.
Brown County, located in Southeastern Indiana draws visitors each year as the sandstone formations, known as the Borden Group, display beautiful formations of bedrock throughout valleys and steep-sided hills.
Chert is composed of cryptocrystalline quartz or microcrystalline.
It is a fine-grained sedimentary rock.
Crypto stands for “hidden” and describes the tiny quartz crystals that are too small to see with the human eye.
Also known as Indiana hornstone, Chert was great material for Native Americans to make arrowheads, spear points, and other stone tools.
A variety of colors can be found in Chert depending on the mineral and organic matter of exposure.
From white, tan, and brown to red, dark gray, and black, the environment and iron oxides create different hues.
The two properties of Chert that separate it from other hard sedimentary species is its ability to break with a conchoidal fracture to form unusually sharp edges and its 7.0 rating on the Mohs Hardness Scale.
Chert can only be found in certain areas of the world.
Australia, England and France have mines.
In the United States, Arkansas and Indiana are known for their ample supply of Chert.
In the French Lick area of Southern Indiana, the Lost River Chert is well exposed and is bluish-gray from leached carbonate.
There are different types of limestone.
Bedford limestone, or Indiana limestone, is one of the purest quality with 97% calcite.
Bedford is a town situated 70 miles of Indianapolis, Indiana, and is considered to be “the Limestone Capital of the World”.
Limestone of this area was used to build the Empire State Building and The Pentagon.
The building stone quarried in Southern Indiana consists of light-gray to bluish-gray limestone (calcarenite) that has oxidized locally to a light tan.
It is medium-grained and porous. It consists mostly of fossil fragments and small fossils.
Indiana limestone is a wonderful building material due to the following qualities:
- More durable than typical limestone
- Can be cut into very large blocks
- Can hold fine detail when carved
Limestone was named as the state stone of Indiana in 1971.
Dolomite is similar to limestone and can be found in Indiana.
It is a mineral and a rock and is also found in sedimentary basins worldwide.
One of the largest specimens of dolomite is located in Italy where the Dolomite Mountains and Dolomitic Alps cover the northeastern part of the country.
Dolomite and limestone are close in characteristics, although dolomite is believed to be formed from lime mud in magnesium-rich groundwater.
They share the same color hues of white-to-gray and white-to-light brown with occasional black, green, or red appearing.
Dolomite is harder than limestone and is used in the production of asphalt paving and other construction projects.
The upper Salamonie River in northern Indiana holds dolomite of outstanding purity. Meshberger Bros.
Stone Corp. quarry of Portland is mainly responsible for their exposure.
Dolostone is made from dolomite and has the same qualities as limestone.
It has a high calcium and magnesium content.
Some geologists refer to dolostone and dolomite as one and the same.
Siltstone, also called aleurolite, is hardened sedimentary rock made up of silt particles.
These tiny particles measure from 0.00015 to 0.0025 inch and are hard and durable.
It is different from sandstone because the pores are smaller. Siltstone only forms underwater.
The properties of siltstone include:
- Uniform in appearance
- Blue-gray to dark green in hue
Indiana siltstone, along with limestone, can be found in the vicinity of Bloomingrton, Indiana.
Indiana siltstone contains a high concentration of durable silica particles.
It is much harder than the surrounding limestone.
The main purpose for siltstone is in the manufacture of making cement.
Shale is a rock made up of more than 50 percent clay.
It also holds substantial amounts of quartz, along with feldspars, iron oxides, and other minerals in various quantities (depending on where in the world it was formed).
It is formed when silt and clay are compressed.
Composed of many layers, it splits into narrow pieces where these layers connect, making it very brittle.
New Albany Shale in Indiana is located north of Cincinnati and is brown, black, and green in color.
Shale gas is found trapped within the shale formations and is a good source of natural gas in the area.
Canada also has large deposits of shale.
Shale is also important in the manufacture of brick, pottery. Portland cement and tile.
Gypsum consists mostly of calcium sulfate dihydrate, though you might find anhydrite, clay, or limestone (among other materials in small quantities) mixed in.
It can be found worldwide, but is plentiful in Indiana.
Mined west of the Mississippi River, gypsum has been duplicated through synthetic means for cost-saving purposes.
Gypsum is also used in the production of cement and for agricultural applications, where it acts as a soil amendment, a conditioner and a fertilizer.
Smaller quantities of high-purity gypsum are used in glassmaking and metal smelting.
Indiana is rich in sedimentary rocks that have been formed over thousands of years.
Bedrock is important in the continuing ecology of the world and Indiana is a large contributor of the Earth’s nitrogen cycle.