Treasures from the beaches of Sedar Bay (Part 3)

Wayne W Sukow PhD and David L Schuder BA (USA)

This is the last of three articles on the beaches of Sedar Bay. The first largely covered the geology of the area, the second discussed collecting minerals from the region, whereas this will cover the collection of fossils.

Fossils from Sedar Bay

Few people know about them, but you can also find an array of fossils on the shore of Sedar Bay – horn corals, the coral Favosites, crinoids and, rarely, Petoskey stones. Some of the granular jaspers started as algae and/or bacteria and a few that are not yet identified look like worm tubes. Some have been agatized, with fortifications showing in them. Most must have been moved to this location by one or more of the glaciers that have passed over the lake as discussed earlier or originated in the Hudson Bay lowlands 40 million years ago. Figs. 12a-e tell the very short story. Not surprisingly, all pebbles with fossils are weathered by the action of Lake Superior, with its endlessly rolling fresh waters over many years.

Fig. 12a. The cross-section, with its unusual white radial structures, suggests this is an agatized crinoid head. You can see a pistil in the right hand side of the polished face.

Fig. 12b. Perhaps tiny petrified marine organisms make up this Sedar Bay hematite pebble.

Fig. 12c. Sedar Bay fossils, which contain or are composed of two different fossils, are rare. Although this one is only black, grey and white, the organisation and cellular structures in the centre is striking.

Fig. 12d. A close up of Fig. 12c showing more detail. The open chamber structure on the upper right is not explained. Could it be a worm tube? At any rate, the cellular structures in the centre suggest that a marine organism cohabited inside the fossil coral.

Fig. 12e. A fossilised horn coral. The corals were brought to the area by one of the glaciers from the Hudson Bay lowlands, millions of years ago.

Fig. 12f. Another horn coral, with only part of its centre showing the cellular structure. The rest is filled with grey-white chalcedony.

Finally, there are pebbles found at Sedar Bay that are hard enough to take a polish and these include flints, granites and basalts. The Fig. 13 sequence again tells a short story and we begin with unakite and patricanite. In some areas of the USA, unakite is considered a semi-precious gem because of its interesting mixture of red-orange from feldspars and green colours from epidote, along with sufficient hardness for it to take an excellent polish. It also is the state stone of Virginia.

Fig. 13a. A two inch pebble of unakite is not uncommon, but this piece is special as it has two inclusions of cubic pyrite crystals that were identified by Tom Rosemeyer.

You will notice that we do not give the size of any of the specimens pictured in this article. The reason for this is that they are generally between a quarter and a silver-dollar in size. Besides, we want the reader to focus on the detail that can be seen in each specimen and, for that reason, many are magnified slightly by between two and six times. In addition, since all the specimens have been tumbled by the waves and currents along the bottom of Lake Superior, there are no husks, except for the few instances where the agate is partially surrounded by basalt matrix.

Fig. 13b. The pyrite crystal is damaged, but it’s clearly a cubic crystal along with some interesting striations. (From the collection of EV and Sue Duester.)

This ends our excursion to the beaches of Sedar Bay. We hope the trek through gemstones that polish and unexpected finds has stirred your interest, and the next time that you are in Upper Michigan’s Copper Country, you take the small side trip out of Calumet to Sedar Bay and find some for yourself. We also encourage you to share your finds, especially the rare and the unusual, with other rock hounds that frequent the region and those in your home mineral club.

Fig. 13c. The subtle pinks and greens of patricianite make it a semi-precious gem, especially when it’s solid and has lots of native copper crystal inclusions. It also takes a fine polish and is found in quantity in some of the Copper Country mines waste tips. The rounded edges of this piece indicate it’s been tumbled in Lake Superior.

This article is in memory of Prof Donald Schuder. Before his retirement from Purdue University, Prof Schuder inspired many people, teaching them the joy of mineral collecting and the quest to learn and understand the gifts that nature has provided us. As one student said, “He was a true teacher and encouraged me to study the world of minerals, and to see and not just look.” He was an avid mineral collector, collecting on the many beaches of the Keweenaw Peninsula (see Fig. 4.b) and from the waste tips of the area’s copper mines.

Acknowledgements

All but a few of the Sedar Bay mineral treasures shown in this article were collected by Dr Donald Schuder (deceased), who taught at Purdue University, his wife Mary and his son, David Schuder, who is co-author of this article. Also, Sam Norwood’s Sedar Bay collection is well represented.

We are indebted to Dr George Robinson, curator of the Seaman Mineral Museum at Michigan Technological University, Dr Gene LaBerge, geologist at the University of Wisconsin-Oshkosh, and Tom Rosmeyer, the former geologist at the Camp Bird Gold Mine in Colorado. Thanks also go to John Marshall, who started all this a few years back and his editing skills. All photo images are by David Schuder.