Pebble beach below the Grand Sable Dunes at Sable Falls on Lake Superior — Pebble beach at Sable Falls, Lake Superior Photo: National Park Service, Public domain

A free, neutral guide to Michigan geology

Every beach stone in Michigan has a backstory.

Ancient volcanoes, warm tropical seas and ice up to a mile thick all left pieces behind. Learn how the state was built, then go find the rocks that tell the story.

Start exploring Identify a rock

Start here

How Michigan was built

Read the seven chapters See the bedrock map

Where to hunt

Open the rock hunting map: 57 spots, pick a rock, bedrock layer

Quick facts

1965Michigan made the Petoskey stone its state stone (Public Act 89 of 1965).¹⁶
State gemChlorastrolite (greenstone), adopted by Act 56 of 1972, effective March 30, 1973.⁹
All the way to IowaGlaciers carried chunks of puddingstone's Ontario source rock as far as Southwest Iowa.¹³
76 spotsin 7 regions, each named by an official source.

Can I keep it?

It depends on whose land you are on.

Read the full rules

Sources (16)

Sleeping Bear Dunes National Lakeshore (NPS), Beaches. https://www.nps.gov/slbe/learn/nature/beaches.htm (checked October 21, 2026)
Michigan EGLE, Fossils. https://www.michigan.gov/egle/public/learn/geology/rockhounding/fossils (checked October 21, 2026)
University of Michigan Museum of Paleontology, Hexagonaria percarinatum. https://lsa.umich.edu/paleontology/resources/beyond-exhibits/hexagonaria-percarinatum.html (checked October 21, 2026)
Michigan EGLE, Rockhounding. https://www.michigan.gov/egle/public/learn/geology/rockhounding (checked October 21, 2026)
Minnesota DNR, Lake Superior agate. https://www.dnr.state.mn.us/snapshots/rocks_minerals/lakesuperioragate.html (checked October 21, 2026)
A. E. Seaman Mineral Museum (Michigan Tech), Float Copper, Web Publication 3 (PDF). https://museum.mtu.edu/sites/default/files/2019-11/AESMM_Web_Pub_3_Float_%20Copper.pdf (checked October 21, 2026)
A. E. Seaman Mineral Museum (Michigan Tech), Copper (PDF). https://museum.mtu.edu/pdfs/COPPER.pdf (checked October 21, 2026)
A. E. Seaman Mineral Museum (Michigan Tech), Keweenaw Mineral Collecting guide (PDF). https://museum.mtu.edu/sites/default/files/2022-04/Keweenaw%20Mineral%20Collecting.pdf (checked October 21, 2026)
Michigan Compiled Laws, MCL 2.17 (state gem). https://www.legislature.mi.gov/Laws/MCL?objectName=mcl-2-17 (checked October 21, 2026)
Michigan EGLE, state gem (chlorastrolite) handout (PDF). https://www.michigan.gov/-/media/Project/Websites/egle/Documents/Programs/GRMD/Catalog/04/GIMDL-GGGS.PDF (checked October 21, 2026)
Isle Royale National Park (NPS), Laws and Policies. https://www.nps.gov/isro/learn/management/lawsandpolicies.htm (checked October 21, 2026)
Michigan State University, Puddingstones. https://project.geo.msu.edu/geogmich/puddingstones.html (checked October 21, 2026)
University of Waterloo Earth Sciences Museum, Lorrain Formation jasper conglomerate. https://uwaterloo.ca/earth-sciences-museum/peter-russell-rock-garden/1-lorrain-formation-jasper-conglomerate (checked October 21, 2026)
Illinois State Geological Survey, Conglomerate. https://resources.isgs.illinois.edu/outreach/geology-resources/conglomerate (checked October 21, 2026)
University of Michigan Online Repository of Fossils, Michigan backyard fossils: corals. https://umorf.ummp.lsa.umich.edu/wp/mi-backyard-fossils-corals/ (checked October 21, 2026)
Michigan Compiled Laws, MCL 2.16 (state stone). https://www.legislature.mi.gov/Laws/MCL?objectName=mcl-2-16 (checked October 21, 2026)