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Rock and mineral identification

A stack of rocks on a lakeshore at sunset; the stones have glowing yellow flecks
Environment, Great Lakes, and Energy

Rock and mineral identification

Love rocks? So do our over 70 geologists working throughout our programs! One of the more fun advantages to having geologists on staff is we always have someone to call when we need help identifying a cool rock we found. 

Our geologists have helped identify several interesting Michigan finds over the years, and have provided some rockhounding tips to help you find treasures of your own.

We 'dig' these stories from our geologists!

  • This content was originally posted as a MI Environment article in 2024 and was written by Mary Ann St. Antoine, a senior environmental quality analyst in the Marquette District Office of the Michigan Department of Environment, Great Lakes, and Energy (EGLE). St. Antoine offers tips on how to find and identify agates, an ornamental stone.

    July 1, 2024 - Michigan rock hounding is a favorite pastime for locals and tourists alike. There are so many pretty, colorful, lake smoothed pebbles found on the beaches of the Great Lakes. One of the most coveted pebbles is the elusive Lake Superior agate.

    What actually is an agate?

    Agates are colorful banded rocks which are mainly composed of chalcedony – a variety of quartz. They’re formed when gas bubbles in lava leave a hole or “vesicle” in the rock. Silica rich solutions flow into the hole in the host rock and fill it up over time, making the bands. Different chemicals in the silica rich solution cause bands to be different colors. The volcanic rock is weathered away and the harder agates are released from the softer host rock.

    Agates are sometimes hard to identify, even for the experts. I found my favorite agate in Grand Marais. It was rusty brown, pock marked with no bands on the outside. I almost threw it away as a dud. I was so excited when I took it out of the tumbler, and it was the most beautiful banded purple amethyst!

    The bright bands are a dead giveaway but usually the inside vibrant bands in the agate can’t be seen from the unpolished outside of the rock. Look for a dull waxy luster. Often, they are red, orange or brown with a pock-marked surface. Agates are translucent. Sometimes this is hard to tell from the outside - hold them up to the light and see if they transmit a little light.

    Where can I find agates?

    Find a Lake Superior beach that has lots of exposed pebbles. A good time to look is after a storm when the waves have washed up new pebbles. Some of my favorite agate places in the Upper Peninsula of Michigan are Whitefish Point in Paradise, Muskallonge State Park north of Newberry, Grand Marais Beach, Bay Furnace Beach in Munising, Pebble or Dog Beach in Marquette, Agate Beach and Misery Bay in Toivola, Black River Harbor Beach in Ironwood, and Eagle River Beach in the Keweenaw.

    Agates can also be found in rivers with pebbles and in gravel quarries. Surprisingly, many beautiful agates have been found in the landscaping pebbles at shopping centers!

    Spend an afternoon walking along a sunny Michigan beach picking pretty pebbles. Maybe you’ll find a keeper.

    If you’re not in the mood for looking for agates but would like to see some beautiful specimens, the A.E. Seaman Mineral Museum located on the campus of Michigan Technological University in Houghton has world’s best collection of Michigan minerals including many beautiful agates. The Ernest Kemp Mineral Resources Museum on the campus of Lake Superior State University in Sault Ste. Marie has many specimens from all over the world as well as many unique local varieties of minerals including agates.

    Quiz: Is it an agate?

     

    Happy hunting!

  • June 5, 2023 - Yooperlite® is a fluorescent rock (Sodalite syenite) that glows “in the dark” under ultraviolet light. The rock first became known when a U.P. resident discovered them in 2017. 

    Rob Wolfe, an environmental quality analyst in our Marquette District Office, has been a rockhound in Michigan’s Upper Peninsula for 50 years and has some tips on how to find Yooperlite® on your next trip. 

     

    Types of Yooperlite®

    In normal light, a Yooperlite® looks like granite. Sodalite replaces quartz, so the larger the mineral size, the brighter the shine. There are roughly five classes of Yooperlites:

    • Gemmy (mostly Sodalite or large sodalite crystal, the entire specimen glows orange)
    • Snowflake or Flower (similar to snowflake obsidian, large blotches on the surface that look like snowflakes, but crystal glow does not penetrate into the interior)
    • Striated (sodalite fills cracks in the rock matrix, so appears as orange lines or veins)
    • Spray Paint (tiny crystal droplets scattered around the surface)
    • Galaxy (larger crystals than spray paint that are dispersed in the rock that glow like the night sky, crystals penetrate the matrix)

    Sizes of Yooperlites®

    “The largest was about the size of a baseball, but I would say based on the size of gravel where I search, most are the size of a ‘pinky nail’ to thumbnail length,” Wolfe notes. “I have seen cantaloupe-sized ones found in Houghton County or from divers. There is a limit to how much one can take from public beaches.”

    Where to look for Yooperlites®

    Yooperlites® can be found as loose pebbles and cobbles along many Lake Superior beaches and even in some inland gravel pits, but you won't find large rock outcroppings of them here in Michigan -- Yooperlites are actually from Canada! They are derived from igneous rocks near Marathon, Ontario known as the Coldwell Alkaline Complex and were transported into Michigan by glaciers during periods of continental glaciation.

    • Start with a beach that has known stones (providing you have permission and it is legal to collect there)
    • Get a good light (365 wavelength; Rob Wolfe says his are Convoy brand)
    • Wear safety glasses with UV protection (some people are not courteous when shining lights; be conscious of where your light is shining at all times)
    • Take along a garden tine rake to move the deposited gravel around or to reach out into the water. Yooperlites may not shine on all surfaces, so moving stones around will increase your chance of seeing them if they were not right at the surface or orientation.
    • Be strategic: Wolfe says he "typically carries two lights (one in each hand) and cross the combined beams using a sweeping side-to-side motion for better coverage and light angle about 6 to 8 feet in front"
    • With the right light and safety equipment, they will be bright, so you do not need to walk slowly thinking you will miss them.  Walk at a normal pace and shine the light with a sweeping motion.
  • January 4, 2022 - When Adventure Mining Company, a mine tour company in the Upper Peninsula town of Greenland, Mich., had recently pumped water out of the mine's subterranean third level, they spotted a bright blue mysterious mineral. It got the attention of MLive which featured a story about it, and the story quickly spread internationally. Commenters on social media offered their guesses as to what it may be.

    It's unclear if the company is pursuing identification of the mystery material, but Melanie Humphrey, geologist at the Michigan Department of Environment, Great Lakes, and Energy's (EGLE) Upper Peninsula Geological Repository, known as a rock library, says said there are a number of methods that can be used to get clues. Find these identification methods listed out lower on this page!

    "Identifying physical properties can give clues about the chemical composition of a mineral," Humphrey noted. "However, a trip to the lab to perform analytical techniques that will provide the specific chemical makeup affords assurance of the identification of a mineral and is the only way to confirm discovery of a new one."

    So far, the mineral has not been positively identified, although the mine company says it is a "secondary mineral that is caused by a reaction with air and water." Humphrey speculates it may be azurite, as it is associated with copper ores and can occur as bright blue. However, she cautions that color alone is not conclusive for identification.

  • August 3, 2020 - Back in 2020, WBCK-FM in Battle Creek asked listeners to help identify a rock found on the shores of Lake Huron, near Harrisville. 

    After reaching out to multiple experts to no avail, the next move was to find a geologist and ask their opinion. Before that happened, Mary Ann St. Antoine, one of our staff geologists, happened upon the WBCK article and was able to solve the mystery!

    "Looks like a pyrite concretion (also known as a pyrite nodule). It appears that there may be a fossil - a crinoid calyx where the pyrite has replaced the original mineral. Pyrite replacement in fossils is common in the Devonian shale in Sylvania, OH." said Mary Ann. She also provided information on how to store her find, inside rice or silica packets to keep it from rusting.

    Mary Ann, an avid geologist, has been passionate about rocks for decades. We sat down with her to learn more about her passion about Michigan geology. This content was originally posted as a MI Environment article in 2020.

    How long have you been interested in geology?

    I absolutely love geology and my family and friends complain because all vacations turn into geology field trips. When you look at the geology, it's everywhere and I see things that I find so exciting everywhere I go. Unfortunately, not everybody shares my excitement!

    I graduated in 1990 from Lake Superior State University (LSSU) with bachelor's degree in geology. They have an excellent geology program — all their sciences really. I grew up in Toledo and my father took us fossil hunting in the area and that's where I first saw the pyrite replaced fossils (similar to the rock that Tina found.) The identification of the rock is not a big deal at all — any geologist would have recognized it.

    How did geology become part of your career?

    My grandmother was from St. Ignace and we spent summers in the Upper Peninsula (U.P.) and I cried when I had to go home. I love the U.P., and it is one of the most beautiful places in the world. I moved to St. Ignace in 1976, married a local and raised my children here.

    I worked at LMAS (Luce, Mackinac, Alger, Schoolcraft counties) District Health Department in Mackinac County in drinking water (geology related) in the 90s and then I worked at LSSU as the science lab manager for 15 years. I also worked as adjunct faculty teaching geology labs.
    LSSU has a very field intensive curriculum and I went on most of their field trips — Ontario, Wisconsin, Appalachians, New Mexico, Arizona, Texas, Nevada, South Dakota, Wyoming, Montana, and California — and I really got to understand geology over the years.

    I started at EGLE in 2014. It was a hard decision to leave LSSU as I loved working around the young people. I am an environmental quality analyst here at EGLE and part of my job is hazardous waste (which I also did at LSSU) but part of my job is as a geologist for landfills. EGLE is the best employer — ever! They offer Plan C which allows employees to take of leave of absence up to three months. So LSSU picks me up as a contract employee and I still go on a yearly LSSU field geology trip in May.

    How did you learn of the quest to find out what the mystery rock is?

    I saw the article when it popped up on my news feed for "Michigan News" and I quickly emailed her the answer to her question about her rock. I never thought it would cause so much hoopla! Pyrite nodules (or concretions) are pretty common. Pyritization of fossils is common in some areas of the Midwest — like the Devonian shale where I grew up in northwest Ohio. I had pyritized trilobites and brachiopods that I had collected as a child. I lived in a swampy area in the eastern U.P., and they rusted so I warned the woman in the article about long-term storage of her rock. Her find is very beautiful, and I haven't ever seen one just like that before.

    Are you a rock collector?

    I'm not a big rock collector compared to some people. I had a friend that taught 5th grade science and the rocks that I collected on field trips, I gave to her for her student display. I do pick few agates and pretty rocks along the beach and I collect "omars" (omarolluks) — a graywacke that has a hemispherical void from where a concretion dissolved. They just look cool.

    What advice do you have for people who are interested in rock collecting?

    My advice to anybody that is interested in collecting rocks is to always look down. I have found some beautiful agates in parking lot gravel. Rocks also show up in the most unexpected places.

    The State of Michigan has lots of information on the web about geology and is a wonderful resource. A great book for laymen, available in many libraries, is Geology of Michigan by John A. Dorr and Donald F. Eschman. If anybody is interested in geology, I recommend it as a career, and LSSU has great program.

Techniques for identifying rocks

No matter the rock or mineral, you can count on these rock identification techniques to help you identify your find. Most common minerals can be identified by their basic physical properties in the field, such as:

Multicolored pebbles
  • Color (also color of a "streak" if it can be made by swiping the specimen on a piece of porcelain, creating a powder)
  • Luster (shiny, dull, glassy)
  • Fluorescence (shines under UV light)
Six various minerals on a white background
  • Shape/structure (crystal form or amorphous?)
  • Breakage (how does it break apart, cleavage or fracture?)
  • Density/specific gravity (can get an idea by "hefting" to see if it's heavy for its size)
Pebbles stacked together
  • Magnetism
  • Smell (yes, some minerals have a distinct smell!)
  • Radioactivity
  • Taste (not recommended to perform this test due to safety concerns)

General rockhounding guidance

Follow all rock collecting rules - annual limit is 25lbs total per person per year on state-owned land.

Check for local rock collecting rules.

Get permission if on private land.

Go early in the season when cooler temperatures keep most people off the shoreline.

Go immediately after a storm, as new material is washed up -- do NOT go during the storm or when there's high wave action.

Look along the shoreline, out into the water, and at the high water mark.

Look behind you, as your feet may shift stones as you walk.

Use a hand rake to move gravel around or reach out into the water.

Be respectful of other visitors and the land - pick up trash and Leave No Trace

Be willing to share your tips with others as many are first time searchers - we all remember the joy of our first find!

Have a rock that mystifies you?

Reach out to Melanie Humphrey at HumphreyM@Michigan.gov with information about your find.

Melanie is one of many geologists with our rock library, the Upper Peninsula Geological Repository.

Bring your love of rocks to work!

Many of our positions require some educational background in geology. With a wide variety of positions throughout the State of Michigan and across our many agencies, the perfect career may be waiting for you!

Search for state geology jobs