Illinois State Rock & Mineral: Dolostone, Fluorite

Illinois's state rock is dolostone, adopted in 2022. Illinois's state mineral is fluorite, adopted in 1965. Illinois's state fossil is the Tully monster (Tullimonstrum gregarium), adopted in 1989.

Symbol names and dates are taken from primary state sources linked below. Informal or proposed symbols are not listed unless adopted.

Dolostone specimen — Dolostone (not necessarily from Illinois). Photo: James St. John, CC BY 2.0, via Wikimedia Commons

State rock: Dolostone

Adopted:: 2022

Dolostone is a sedimentary rock with a Mohs hardness of about 3.5–4 and a dull to sugary luster, usually gray, white or brown.

How to identify dolostone →

Often confused with: Limestone, Marble

Fluorite specimen — Fluorite (not necessarily from Illinois). Photo: CarlesMillan, CC BY-SA 3.0, via Wikimedia Commons

State mineral: Fluorite

Adopted:: 1965

Fluorite is a mineral (CaF₂) with a Mohs hardness of 4 and a vitreous luster, usually purple, green, blue, yellow or colorless.

How to identify fluorite →

Often confused with: Amethyst, Calcite, Chabazite

State fossil: Tully monster (Tullimonstrum gregarium)

Adopted:: 1989

Illinois state symbols FAQ

What is the state rock of Illinois?

Illinois's state rock is dolostone, adopted in 2022.

What is the state mineral of Illinois?

Illinois's state mineral is fluorite, adopted in 1965.

What is the state fossil of Illinois?

Illinois's state fossil is the Tully monster (Tullimonstrum gregarium), adopted in 1989.

Sources

We cite primary sources (statutes, state government pages, federal regulations, and land-manager sites). Third-party listicles are not used as citations.

State Designations Act (5 ILCS 460) — Illinois General Assembly (accessed 2026-10-24).
Illinois State Symbols — Illinois Department of Natural Resources (accessed 2026-10-24).

Last verified 2026-10-24. Corrections welcome: if a statute has changed, tell us and we'll re-verify.

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