When bentonite becomes wet, it soaks up water like a sponge and turns into a greasy mud that is very easy to slip on while hiking. While there are many examples of bentonite in the badlands, it is best exposed around Dorothy. A thick bed can be traced for several kilometres along the banks of the Red Deer River. It is so widespread in Alberta that bentonite has become a useful tool for dating rock layers.
Bentonite is composed mainly of montmorillonite, a clay mineral produced by the chemical alteration of volcanic ash. Around 70 million years ago, plate collisions caused numerous active volcanoes likely around Yellowstone and southern British Columbia. These were ash laden eruptions, similar to Mt. St. Helens where the ash was blown over huge areas. The ash settled over much of present day Western Canada. It landed on the saltwater Cretaceous sea, marshy shores and dry land. The ash that landed in the water was more likely to become thick bentonite beds than the ash on dry land.
After absorbing water, montmorillonite can swell to 10 times its dry volume becoming a slippery, greasy clay. Wet bentonite underground can act as a lubricant that promotes slumping along river valleys. As such, it plays an important role in the erosion of the badlands and the formation of the unique landscape.
Historically, it was used by Aboriginals and at Hudson’s Bay Company posts as soap because it could be worked into a lather. Other modern uses include applications as an animal feed binder, foundry sand binder and stucco/mortar plasticizer. The most important use in Alberta is for drilling mud, where the swelling properties make it ideal for sealing porous rocks.
The 10 metre think bed near Dorothy is the thickest and most extensive in Alberta. Paradoxically, impurities in this bed make it low grade and it has not been mined. Therefore all bentonite used in Alberta today is imported.
In order to log this EarthCache, please send me an email (through my geocaching profile, kindly do not post in your log) the answers to the following questions:
On the first line of the email, please include the text “GC2ZP1Z - Dorothy's Popcorn - Bentonite EarthCache"
1. What is the main mineral component of bentonite?
2. How was bentonite used historically?
3. Please provide observations of your visit, was it a dry day? Has there been any recent precipitation? How large are the ‘popcorn’ pieces?
4. Photos at the cache site are always appreciated but no longer a requirement to log an EarthCache.
There is no need to wait for me to respond, please submit your answers and log at the same time. Posted logs that do not have the associated answers emailed within seven (7) days will be deleted. Please feel free to re-post once the answers have been sent.
Remember, there is no physical container to be found for an EarthCache site.
References:
1. A Traveller's Guide to Geological Wonders in Alberta by Ron Mussieux and Marilyn Nelson
2. Canadian Clay Products, Inc. http://www.canadianclay.com/bentonite.htm
