Beach ComBing
the north shore
Rockhounding on Lake Superior
Is this an agate?
The rugged, rocky North Shore of Lake Superior showcases a diverse rock collection created by millions of years old lava that once flowed through our region.
Rocks are plentiful around Lake Superior, and you will find new ones every day as the waves crash the shore. Explore the shoreline at all nine major beaches in Lake County to find various geological makeups.
There are all sorts of rocks along the Lake Superior shoreline! Below, you’ll learn about the most common types of stones and how to identify their geology.
GB Leighton Scopes out Agates on the North Shore
what types of rocks CAN YOU FIND ON THE NORTH SHORE OF LAKE SUPERIOR?
Basalt and Rhyolite are the most common rocks on Lake Superior’s North Shore beaches and originate from lava that cooled quickly on the surface 1.1 billion years ago during the Precambrian era. During this time, North America nearly split in half, causing enormous amounts of lava to spew from rifts, which depressed the land and formed Lake Superior’s basin.
Today, when you explore Superior’s rugged rocky shoreline, know that almost every cliff, ridge, and ledge formed from these ancient lava flows.
How to Identify Basalt: Look for bluish-black stones with tiny crystals. Basalt comes in various sizes and shapes, from round to flat, making an excellent skipping stone!
Rhyolite, a pinkish, sandy-colored version of Basalt, is abundant at Iona’s Beach near Two Harbors. Like Basalt, it formed from quickly cooling lava. Rhyolite is rich in silica and potassium, while basalt lacks these minerals but contains iron and other minerals.
Granite forms deep below the earth’s surface and cools slowly, forming large embedded crystals that include minerals like quartz, feldspar, and mica. Its appearance is coarse-grained and speckled. Although it looks different, its composition is similar to rhyolite – rich in silica and low in iron.
How to Identify Granite: look for rocks with small-medium speckles and varying colors.
Gabbro, although resembles granite it its speckled appearance, Gabbro is closely related to Basalt, except that it cools slowly like rhyolite. It’s colors range from black to gray or a mixture of black and light-colored crystals, such as the example demonstrates.
How to Identify Gabbro: look for black and white flecked, course stones.
Diabase is a hybrid rock composed of basalt and gabbro. Basalt results from lava that cools quickly, while gabbro forms from magma cooling slowly deep within the earth. Diabase occurs in between, cooling at a slow-medium pace and closer to the surface. It has a medium-grain texture with smaller crystals than granite or basalt.
How to Identify Diabase: look for black and white stones with smaller crystals.
Slate is a metamorphic rock formed by heat and pressure on shale. Its color is black to gray, smooth, somewhat shiny, and generally flat. It commonly contains layering. Like basalt, slate often makes a great skipping rock!
How to Identify Slate: look for a smooth black/gray rock that may have some layers. It does not contain crystals.
Gneiss, also a metamorphic rock, looks much like granite but can be more fine-grained. Its distinction are the the bands or stripes of minerals with alternating layers that form within the stone.
How to Identify Gneiss: Look for rocks that look striped and contain layers of different minerals. It may contain specs.
HUNTING FOR AGATES
Of course, agates are the most hunted and coveted rock on the North Shore. Their distinct beauty, scarcity, and the challenge to spot an agate among hundreds of rocks make them more alluring. Each agate is unique; even slabs cut from the same specimen will vary in color and design.
How do Agates form?
Agates are unique semi-precious gemstones that develop when an empty pocket inside a host rock fills up with microcrystals, forming concentric bands or other patterns.
Most agates develop in ancient volcanic lava and are secondary deposits in hollow cavities. These cavities are filled with fluid rich in dissolved quartz molecules and mineral impurities. As the silica concentration becomes supersaturated, it forms fibrous microcrystals that create the distinctive banding of agates.
Each agate is unique; even slabs cut from the same specimen will vary in color and design.
TYPES of Lake Superior Agates
Hover over agate images to learn its type and how it forms.
Best Rock Hunting beaches on the north shore
Agate Bay Beach
Burlington Bay Beach
Crystal Bay Beach & Sea Cave
Iona’s Beach Scientific & Natural Area
Kelsey Beach
Knife River Marina & Beach
Flood Bay Beach Wayside
Thompson Beach
Beaver Bay Agate Shop and Museum
If you tire of treasure hunting for a prize-worthy Lake Superior agate, your best bet is to stop into the Beaver Bay Agate shop – the oldest rock shop in the US!
Here, you’ll find a vast collection of agates of all different shapes, sizes, colors, and patterns to admire. Additionally, they sell jewelry, rough/polished rocks, art, and gifts.
If you were unlucky in your beachcombing efforts, you can purchase a beautiful agate to remind you of the North Shore.