RocksdayMichigan State Stone & Gem: Petoskey stone, Chlorastrolite
Michigan's state stone is the Petoskey stone, adopted in 1965. Michigan's state gem is chlorastrolite, adopted in 1972. Michigan's official state fossil is the mastodon (Mammut americanum), adopted in 2002.
Symbol names and dates are taken from primary state sources linked below. Informal or proposed symbols are not listed unless adopted.
State stone: Petoskey stone
- Adopted:
- 1965
- Law:
- MCL 2.16; 1965 PA 89, effective March 31, 1966
Petoskey stone is a fossil with a Mohs hardness of about 3–4 and a dull luster, usually gray or brown.
The state symbols page identifies it as fossil coral, Hexagonaria percarinata, from reefs about 350 million years old.
Where in Michigan: Northern Lower Peninsula.
How to identify Petoskey stone →
Often confused with: Crinoid, Horn Coral
State gem: Chlorastrolite
- Adopted:
- 1972
- Law:
- MCL 2.17; 1972 PA 56, effective March 30, 1973
- Variety:
- greenstone (Isle Royale greenstone)
The statute adopts chlorastrolite, commonly known as greenstone. The state symbols page also calls it Isle Royale greenstone.
Where in Michigan: Upper Peninsula, including Isle Royale.
Official state fossil: Mastodon (Mammut americanum)
- Adopted:
- 2002
- Law:
- MCL 2.401; 2002 PA 162, effective April 8, 2002
The state symbols page says mastodon fossils have been found at more than 250 places in Michigan.
Michigan state symbols FAQ
What is the state stone of Michigan?
Michigan's state stone is the Petoskey stone, adopted in 1965 (MCL 2.16; 1965 PA 89, effective March 31, 1966).
What is the state gem of Michigan?
Michigan's state gem is chlorastrolite, adopted in 1972 (MCL 2.17; 1972 PA 56, effective March 30, 1973).
What is the official state fossil of Michigan?
Michigan's official state fossil is the mastodon (Mammut americanum), adopted in 2002 (MCL 2.401; 2002 PA 162, effective April 8, 2002).
Is the Petoskey stone a fossil?
Yes. The Petoskey stone is fossilized coral, Hexagonaria percarinata, from reefs that grew about 350 million years ago, according to the State of Michigan.
Sources
We cite primary sources (statutes, state government pages, federal regulations, and land-manager sites). Third-party listicles are not used as citations.
- Michigan Compiled Laws § 2.16, State stone — Michigan Legislature (accessed 2026-10-23).
- 1965 Public Act 89, Petoskey stone as the state stone — Michigan Legislature (accessed 2026-10-23).
- State Facts and Symbols — State of Michigan (accessed 2026-10-23).
- Michigan Compiled Laws § 2.17, State gem — Michigan Legislature (accessed 2026-10-23).
- 1972 Public Act 56, chlorastrolite as the state gem — Michigan Legislature (accessed 2026-10-23).
- Michigan Compiled Laws § 2.401, Official state fossil — Michigan Legislature (accessed 2026-10-23).
- 2002 Public Act 162, mastodon as the official fossil — Michigan Legislature (accessed 2026-10-23).
Last verified 2026-10-23. Corrections welcome: if a statute has changed, tell us and we'll re-verify.
Think you could spot these from a blurry close-up?
Play today's Rocksday