How to Identify Rocks of Michigan
There are three types of rocks. Igneous rocks form deep underground. Metamorphic rocks are formed by high pressure, heat or both. Sedimentary rocks form when other rocks break into small pieces of sand, silt and clay then form new rocks by either being compacted from weight or cemented together by materials, usually minerals, that dissolve in water. You can identify rocks in Michigan by their location, color, texture, patterns and grain.
Other People Are Reading
Instructions
-
-
1
Locate an area that is known for particular rocks. Metamorphic rocks and igneous rocks are only found in the western half of the Upper Peninsula; sedimentary rocks cover the rest Michigan. Sedimentary rocks that were pushed into Michigan by glaciers during the ice age can be found in both peninsulas.
-
2
Look for Michigan's state rock, the Petoskey stone, on beaches, road cuts and in gravel pits in Charlevoix, Cheboygan, Antrim, Presque Isle, Emmett and Alpena counties, the Traverse Bay area between Elk Rapids and Eastport, and Petoskey. The fossilized remains of one species of coral from the sea that once covered Michigan, the Petoskey stone is mostly calcite and is easily carved. It has a six-sided pattern and is gray, tan or brown with darker spots. Most Petoskey stones are smooth and well worn. Spring is the best time to find them.
-
-
3
Find two types of igneous rock--extrusive and intrusive--in the western Upper Peninsula. Extrusive, or volcanic, rocks were liquid magma that erupted from volcanoes and cooled fast. Their crystals are so tiny they usually can't be seen. Find one extrusive rock, basalt, in Houghton. Basalt is dark gray or black and sometimes has gas bubbles. It's hard, fine grained and darker than intrusive rock. Intrusive rocks also started as magma, but they cooled slowly underground. Find one intrusive rock, granite, in the part of the Upper Peninsula west of Marquette. Granite is pink or white with visible interlocking crystals made of quartz and feldspar.
-
4
Search for metamorphic rocks in the western part of the Upper Peninsula. Slate is black, gray, blue-gray, green-gray, brown or red. It's thin and has smooth, straight, flat layers. Slate splits easily into thin, flat pieces and can scratch glass. Look near Marquette for gneiss. It has ribbonlike layers, and the interlocking crystals can be seen. It's usually light colored, but it can be dark. The grains are coarse, lined up and in layers. Gneiss is a hard rock that usually breaks into blocky pieces rather than along the layers.
-
5
Search for a popular Michigan rock, Lake Superior agate, which can be found along the Lake Superior shoreline. Collectors love the rich, red, yellow and orange color caused by oxidation of iron. The banding patterns make Lake Superior agates stand out, and they come in all the colors of the rainbow. Look for rust-red or yellow staining on rocks and a glossy, waxy look on chipped or broken surfaces. A translucent glow can be seen on sunny days from the quartz that's in agate. Some agate stones have an almost perfectly smooth natural surface. Some agate stones have perfectly round bands, or "eyes" on the surface, and some have perfectly straight parallel bands. Agate is a hard rock. Some of the best places in Michigan to look for Lake Superior agate are on the south shores of Lake Superior, in the ridges of the Keweenaw Peninsula and Isle Royale, at Whitefish Point in Newberry northeast of the Tahquamenon Falls, at Grand Marais by the Pictured Rocks, at Great Sand Bay near Eagle Harbor, and at F.J. McLain State Park near Hancock.
-
6
Locate sedimentary rocks anywhere in Michigan. Limestone can be found near Rogers City. It can be tan, yellow, white or gray, or it can have impurities that make it red or black. Limestone often contains fossils. The minerals are mostly calcite, and the crystals can't be seen. The crystals are smooth and fine or medium grained. If you put limestone in white vinegar, it probably will fizz. Sandstone has round grains that are the same size. It can be red to brown, light gray to white, green or yellow. Colors in sandstone layers can vary slightly. Made of quartz sand, the grains are medium. Sandstone can be found near Grand Ledge. Shale, found near Gaylord, can be black, gray, red, brown, blue or dark green and sometimes has yellow or green layers of particles. It's fine grained and smells like mud when it's moist.
-
7
Visit rock shops throughout Michigan that sell rock samples and maps with information on where to find rocks and how to identify them. Rock shops also offer information about rock swaps that have unique specimens of rocks. You also can find guidebooks, tours of mines and rock piles, and you might even be able to sell rocks you've found.
-
8
Make a trip to the Seaman Mineral Museum at Michigan Technological University in Houghton. Minerals from the Lake Superior copper country are on display there. Call 906-487-2572 for hours.
-
1
Tips & Warnings
Buy a field guide of Michigan rocks or check one out from your local library.
Spring is the best time to search for rocks, after the ice is gone.
