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Great Lakes Rocks to Collect Along the Coast All of these Great Lakes rocks and fossils are full of history and beauty can all be found on our regional coastline! From patiently searching for a Lake Superior agate, to finding a beach on Lake Michigan that is full of Petoskey stones, cool and exciting rocks […]
All of these Great Lakes rocks and fossils are full of history and beauty can all be found on our regional coastline! From patiently searching for a Lake Superior agate, to finding a beach on Lake Michigan that is full of Petoskey stones, cool and exciting rocks can be found in every one of the Great Lakes. Happy hunting your favorite Great Lakes Rocks!
Minnesota’s state gemstone! The Lake Superior agate was formed during lava eruptions that occurred about a billion years ago. They are rich in red, orange, and yellow coloring. This color scheme was caused by the oxidation of iron. The concentration of iron and the amount of oxidation determine the color within or between an agate’s bands.
The extinct halysite corals displayed small tubes from which resided the jelly-like coral animals called polyps. The coral polyps contained stinging cells for protection and also grasped plankton food that passed by in the ocean currents. As the corals grew, they built up walls of tube-like chambers called theca which steadily multiplied adding more links to the chain. As they continued to multiply, they built large limestone reef structures on the seabed. They thrived mostly during the Silurian period up to 425 million years ago!
A Petoskey Stone consists of tightly packed, six-sided corallites, which are the skeletons of the once-living cor-al polyps. The dark center (or eyes) were the mouth of the coral. The lines surrounding the eyes were once tentacles which brought food into the mouth. The Petoskey Stone, like the city, was named for the Ottawa Chief Pe-to-se-ga (Rising Sun) because the stones pattern looks like the rays of the sun.
The Charlevoix stone looks a lot like its cousin, the Petoskey stone. It’s smaller in total size, but is especially distinguished by its smaller honeycomb like corallite patterns.
Crinoid fossils look like small discs with holes in their centers, like Cheerios. They are from the stems of an animal that looks a little like a flower, but is really a relative of the starfish. The discs were stacked together to form a long stalk that attaches the animal to the sea floor. The Native Americans used their fragmented fossilized sections to make necklaces and so another common name for them some people use is Indian Bead.
This unique material was a byproduct of the short-lived days of smelting iron ore in Northwestern Michigan. The Upper Peninsula Mesabi iron ranges supplied the ore. A high grade charcoal made only from beech and maple combined with local limestone flux reduced the iron ore to pig iron, creating a unique foundry glass. Smelting began in 1875 and by 1900 had ceased due to lack of hardwood. The byproduct was dumped into Lake Michigan and shows up from time to time on the beaches from Leland to Traverse City.
Favosites consist of a series of calcitic tubes (corallites) packed together as closely as possible, thus the resemblance to a honeycomb. The openings for the coral polyps are much smaller than in Petoskey stones and look like a lace pattern draped over the rock.
The word “granite” comes from the Latin granum, a grain, in reference to the coarse-grained structure of such a holocrystalline rock. These rocks mainly consist of feldspar, quartz, mica, and amphibole minerals.
Horn corals are known as the Rugosa, named so because of a unique horn-shaped chamber with a wrinkled, or rugose, wall. Rugose corals lived on the sea floor or in a reef. They had tentacles to help them catch prey.
Michigans gemstone! It is unique to Isle Royale and a few old copper mines on the Keweenaw Peninsula. The name translates to “Green Star Stone.” It is a gem form of the mineral pumpellyite that filled the tiny gas pockets (vesicles) of the billion year old basalt flows that underlie the Keweenaw and Lake Superior.
They are often known as “lamp shells” and have hard “valves” (shells) on the upper and lower surfaces.
The Michigan Puddingstone is a conglomerate of primarily quartzite and pebbles of jasper. Puddingstone is a type of sedimentary rock which first formed in river channels. During the Ice Age, they were pushed down through Eastern Michigan from Ontario Canada by the glaciers.
