superiortrails superiortrails - shovel point

lake superior agate - the minnesota gemstoneLake Superior Agates, Gem Stones & Rocks
- Part 1
Igneous and Metamorphic Lake Superior Beach Rocks

Meandering along Lake Superior's beaches sorting through the stones and pebbles washed up on the shore is one of my favorite relaxing ways to pass the time . . . doing not much at all. The ultimate prize is finding a Lake Superior Agate. I'll admit right off I've yet to definitely find one. Gotta a candidate or two* but I really won't know for sure until I polish them in the new, but yet to be used, vibrating rock tumbler Joanne got me for Christmas.

A problem with novice rock hounds like myself is the rocks and stones we see on the beach don't look like the ones we find in the shops. They've been tumbled and polished to bring out their beauty. I needed to run into someone on the beach who knows their stones and can help me know what an agate in the rough looks like. (At the 2013 Lake Superior Agate Festival I found lots of these sorts of folks!)

But aside from agates, I find all sorts of neat looking, interestingly shapped rocks along the beach. I rarely come home from a trip to or around the Lake without a box full of rocks. Once I began the habit of collecting rocks, I graduated to trying to learn more about them. I've done some reading in an attempt to better identify what I am finding on the beach. Two sources have been particularly helpful: Sparky Stensaas' "Rock Picker's Guide to Lake Superior's North Shore" and Susan Robinson's "Is this an Agate." (See our recommended Rock Hound books near the bottom of the page)

While these two books have been expertly documented and illustrated, I wish they had shown me actual photographs of the rocks rather than drawings. Which leads to what I am endeavor to accomplish here - giving other rock pickers actual photographs of a number of the rocks, stones, and minerals you are likely to find along the shore.

Armed with Sparky's and/or Susan's book plus some of the pictures and descriptions I've provided here, perhaps will help you ID what you are collecting.

By the way, if you want to print out any of these larger images, just *right click* on the image and choose "copy image" to copy it to your hard drive. Once there you can click on it and print it out.

~~~"Click" on smaller images for a larger picture~~~

Basalt

Basalt is one of the most common rocks you'll find, yet I love their smooth surface and solid feel in my hand. Each one has a distinctive shape and in a variety of shades of color from blush-black to grey. They are volcanic rock formed from lava that quickly cooled when it reached the surface. That quick cooling is what caused it to be dense, very fine grained (tiny crystals) and smooth - although the smooth surface is also due to glacial grinding & Gitche Gumme tossing it about for eons. That Basalt rock you hold in your hand is over a billion years old!

ophitic basalt lake superior

Ophitic Basalt

Ophitic Basalt looks like a basalt rock that has been decorated with lighter colored little painted petals. They come from tiny feldspar crystals that were in the lava. Because the crystals have worn at different rate than the basalt there is often a slight mottled texture to these these stones. This particular specimen has many feldspar crystals, others have fewer and require more close inpsection to see them (look for the little spots that look as if they were put there by dabbing with a paint brush).

rhyolite lake superior

Rhyolite

Rhyolite is a sandy-colored version of Basalt. Formed from quickly cooling lava just like basalt, it is rich in silica and potassium, whereas basalt is poor in these minerals and richer in iron, and other minerals. Coloration of Rhyolite will vary depending upon the mix of silica and iron and some of the trace minerals. Some stones may be a difficult call: basalt or rhyolite?

The sample on the far right may be Rhyolite that has darker bands of flow of an iron-richer form of lava. > > >

vesicular rhyolite lake superior

Vesicular Rhyolite

Frequently the molten lava flowing from deep down in the earth was filled with gases that formed bubbles when the lava cooled - leaving a pock-marked surface on the rock. The sample to the right shows two examples - one with many vesicules and the other with only a few.

A similar process occurs with basalt, forming vesicular basalt. Unfortunately I don't have any samples to show here.

amygdaloidal rhyolite lake superior

Amygdaloidal Rhyolite

Sometimes the holes that create vesicular rhyolite fill up with molten minerals - often calcite and quartz - that form crystals in the cavities when the lava cools into a rock. The crystal spots are always rounded since the holes were formed by gas bubbles.

amygdaloidal basalt lake superior

 

Here is a sample of Amygdaloidal Basalt > > >

Porphitic Basalt

At first glance, a porphitic rock looks like the amygdaloidal rocks pictured above. On closer inspection you'll see the blobs of crystals are rectangular shaped not round. This is because the crystals were already there when the magma was molten. Rhyolite can also occur in a porphitic form.

Granite

Granite is formed deep underground and stays there for a time, cooling slowly. This process forms large crystals and includes minerals like quartz, feldspar and mica embedded within the rock. It is coarse grained and speckled. Although it appears quite different, it is similar in basic composition to rhyolite - rich in silica and poor in iron.

Gabbro

As granite is the coarse grained, slow cooling cousin of rhyolite, gabbro is the coarse cousin of basalt, formed deep underground as granite. My guide books say it can range from black to gray or a mixture of black and light crystals. Sparky says to look for "weathered white flecked" dark, coarse rocks. The white or light gray crystals you see in the sample to the right are weathered plagioclase crystals.

diabase lake superior

Diabase

Here's a rock that is a hybrid of basalt and gabbro - diabase. Basalt results from lava that cools quickly on the surface; gabbro results from magma cooling slowly deep within the earth; diabase occurs in between, cooling medium slowly and closer to the surface. As a result it is medium grained with smaller crystals than either granite or gabbro.

If you hold these guys at an angle to the sun, you can usually see some smaller sparkly crystals reflecting the light.

slate lake superior

Slate

This is a metamorphic rock formed by heat and presure on shale. It is dark to gray in color, smooth, somewhat shiny, and generally flat. Look for some layering. Look closely at this sample and you can see the lighter colored layer sandwich.

gneiss lake superior

Gneiss

Gneiss is also a metamorphic rock. It can be similar in appearance to granite but can be more fine-grained. What is distinctive about gneiss are the bands of minerals that form alternating colors.

red triPart 2 - More Beach Rock & Agate Collecting around Lake Superior.

Books on Lake Superior Agate Hunting & Rock Picking

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Understanding and Finding Agates
Lake Superior Rocks & Minerals: A Field Guide to the Lake Superior Area

Recommended by a SuperiorTrails friend & rock hound, this new guide has actual photographs of various rocks and minerals found on Lake Superior beaches. Co-author Bob Lynch is owner of Agate City Rocks and Gifts in Two Harbors Minnesota

agates inside outAgates Inside Out

Karen Brzys. Director, Gitchee Gumee Agate & History Museum, is an experienced beach comber and agate collector. This is the most comprehensive book I've found on identifying and collecting agates. Most helpful has been the guidance on identifying agates-in-the-rough. [More Info]

Is this an AgateIs this an Agate?: An illustrated guide to Lake Superior's beach stones Michigan

This is required handbook for rock pickers who love to comb Lake Superior beaches looking for pretty rocks and hoping to find an agate. Identifies some of the UP's best rock picking beaches.

Lake Superior Rock Pickers GuideLake Superior Rock Picker's Guide

Here is another book recommended by a Superior Trails reader and rock hound who was able to identify over 50 rocks found on the beach using this guide by Kevin Gauthier and Bruce Mueller. Also included are tips for polishing the stones and rock. Kevin and Bruce also publish a similar guide for Lake Michigan rocks.

Agate Hunting on Lake Superior BeachesAgate Hunting Made Easy: How to Really Find Lake Superior Agates

My wife Jo found this agate hunters book while traveling in the UP and thought it would help her find her first Lake Superior Agate. It is full of tips for agate hunting (and rock picking) and has some very good color photographs of a number of agate variations as well as photos of the other kinds of rocks you'll find on Lake Superior beaches.

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rock pickers guide to lake superiors north shore Rock Pickers Guide to
Lake Superior's North Shore

Sparky's guide covers what north shore beaches to comb, a bit of history on the formation of the various rocks found on beaches, and helpful information and pictures on identifying beach rocks and minerals.

agates: treasures of the earthAgates: Treasures of the Earth

Roger Pabian, professor emeritus at the University of Nebraska-Lincoln, and his fellow authors provide an informative guide to finding and collecting agates.

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2013 Rock On Festival - Lake Superior Agates

agate fest

September 14 -15th Muskallonge Lake State Park
Deer Park, Michigan

We had a great time at the festival. My wife Jo found 5 agates on the beach and is now an addicted agate hound!.

Links for Rock Picking on Lake Superior Beachs and information on Agates and Rocks found around Lake Superior

- Minnesota's State Gem: The Lake Superior Agate

- Minnesota Rocks - Minnesota Geological Society (pdf file)

- Bob's Rock Shop - Online 'Zine for Rock Hounds

- Rock Identification Key - By Don Peck on Rockhounds.com
(I just recently found this site. The key looks real neat and am looking forward to using it on my mystery rocks)

For a nice introduction to rock tumbling, see Cheralyn Maturi's Minnesota Iron Range Website

Marie Frazier, who lives in central Minnesota, has created a number of unique jewelry items from Lake Superior Agates and other gemstones. See her Lake Superior Agate Jewelry Website here.

Continuing your Travel & Trekking
  Around Lake Superior
Superior Trails Lake Superior Circle Tour

 

SuperiorTrails.com - Reinhold Development - 2013


scenic fall color drive report
See when Peak Fall Color is expected to arrive along the scenic Lake Superior Circle Route and our recommended
Scenic Fall Color Drives
.

Camping and Campgrounds Around Lake Superior
Lake Superior Camping
& Campground Directory

Lake Superior Circle Tour Route


Canal Park Brewery Beer Garden
Enjoying lake breezes and views at the Canal Park Brewery Beer Garden - Canal Park.



Best Burgers in Duluth
Follow our Hunt for the
Best Burger
in Duluth, Minnesota.

Pride of Baltimore II Tall ShipTall Ships Duluth Festival

Apostle Islands
See the lighthouses on an Apostle Islands Cruise

Madeline Island Big  Bay Park
Enjoying the great swimming Beach Big Bay State Park on Madeline Island

Travel Information



lake superior circle tour map
Lake Superior Circle Tour Road Map & Guide to Travel Attractions around Lake Superior



Lake Superior Agate?Identifying Lake Superior Agates and Beach Rocks.

Lake Superior Circle Tour Travel Planner


Agate collections on sale
At the Lake Superior Agate Festival

basalt with quartz band
Agate Imposters - Agate Wanna-bees

 

wisconsin michigan color tour map
Upper Peninsual Fall Color
Tour Map

About the Superior Hiking Trail
The Superior Hiking Trail offers some of the best fall color and winter hikes in the midwest.

Golf Courses Around Lake Superior
See our
Reviews of golf courses around Lake Superior