These hills consist of burnt shale that was baked by burning coal waste piles, in this case from the Star Coal Mine just downstream. Baked shale, also known as clinker, can be found throughout Alberta. Where it is plentiful, it is quarried and crushed for use as an ornamental stone.
When coal seams or waste coal piles are exposed, gases are released and the coal may spontaneously combust, ignited by lightning or grass fires. Once the heat reaches around 1000° Celsius, the surrounding rocks begin to bake into clinker which may turn red, orange, purple, black or green. At temperatures above 1117° Celsius, clinker will begin to melt and fuse to form paralava. Paralava is often mistaken for volcanic lava and it often contains some high-temperature igneous minerals. Sometimes paralava will even flow downhill, similar to a volcanic lava flow. The amount of baking or thermal alteration within a single outcrop is variable and a hillside may range from slightly baked clinker to entirely fused and porcelain-like paralava. Most samples however are only partially melted and some red shale may even show signs of its original bedding.
As long as methane and oxygen are available, coal will continue to burn. Some of the coal seams in the Drumheller valley have been burning since 1911 when the coal mines first opened. Once ignited, a burning coal ‘front’ will advance along a coal seam (similar to a grass fire), heating the nearby rock as it goes. Most of the burnt shale in the Drumheller region comes from mine waste. Fine coal that was too small to be trapped on the screens was dumped down hillsides where it mixed with other rock waste from mining operations. The small coal fragments, with a large surface area, have a greater potential for spontaneous combustion.
Burnt shale is often used as an ornamental stone in flower beds and occasionally used as road gravel. It is mined by front end loader and crushed to the desired size. Some shale is also ground quite fine and used as red clay on baseball diamonds.
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 “GC2ZP21 - Rosedale Burnt Shale EarthCache"
1. How many workable seams were on this lease?
2. What was the company name from 1935-1952?
3. Where were the houses moved when the mine closed?
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. Drumheller Rotary Club Signage
