Wednesday, April 22, 2009

Petrified Neapolitan Ice Cream?


These rocks are not really petrified Neapolitan ice cream. They just look a lot like it. Many of us have seen them and not known they are really coal clinkers. They are another interesting Utah geological product.


Clinkers form from burning coal. Anyone who has had one of those old coal burning furnaces will remember the hard black glassy clinkers that have to be removed periodically. Unlike the furnace type, these clinkers form naturally when a coal seam underground catches fire and burns. The interesting colors that often resemble Neapolitan ice cream come from the surrounding rock and its mineral content, mostly iron. The colors will include yellow, red, black and limey green.


These clinkers get their name from the sound they make when struck against another rock or a hammer. The “clink” sound when it is struck resembles the clink sound from striking metal or glass and is caused by the overlaying rock being burned and then collapsing into the slag.


There are places around the world where you can walk up and see into cracks in the ground where the coal is glowing as it burns. Although dangerous, it is an interesting phenomenon to witness.


These coal seams will burn until the coal is gone. In some cases they have been burning for decades and maybe centuries. Many attempts have been made to extinguish these fires but they are to vast. In Alberta, Canada a coal mining company diverted a small river into the mountain to extinguish a burning coal seam. After months of the water running into the mine, the mountain blew up like a volcano spewing ash and steam into the air and sending a mudflow down the mountain.


The problem with a burning coal seam is that once the fire is started cracks in the ground form from the void created as the coal is reduced to ash. These cracks allow air to flow to the fire keeping it fed with a constant flow of oxygen.


Utah has several of these burning coal seams such as the Burning Hills and Smoky Mountains in Kane County. Here the coal seam is about 84 million years old (Late Cretaceous).


There is an exposed clinker seam in Castle Gate that can be seen in a road cut. March 8th, 1824, an explosion in the Number Two Mine at Castle Gate killed 172 miners making this the 3rd worst mining disaster of its time in the U.S. Some of these miners are buried right across the road from the clinker outcrop in the Castle Gate cemetery.


A by-product of burning coal is carbon dioxide. It is estimated that the burning coal seams in China alone produce more carbon dioxide (from fossil fuels) in a year than all the cars and trucks in the United States.

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