And, what happens to coal in extremely deep seams? Does the cola get compressed into something different from anthracite coal? And, why are coal seams accompanied by pockets of methane gas? Wouldn’t this eveolved gas have migrated out ages ago?
Are fossiles commonly found in coal seams?
Postin’ in a coal mine
Goin’ down down down
Postin’ in a coal mine
Whoop! About to slip down
Four o’clock in the mornin’…
Moderator’s Note: Slipping on down on over to General Questions.
Just a quick answer off the top of my head.
I don’t know that there is a definitive answer to this. Some parts of the earth’s crust that used to be close to sea level and covered in plant life are now way, way underground or under the sea. These places, called subduction zones, could have coal down in them at depths of like 30 or 40 km. I don’t know whether anyone’s looked for it at those kinds of depths.
The progression from peat to lignite to bituminous coal to anthracite is more related to age than pressure, but I suppose that you might end up with something like a really, really, impure diamond.
The rock overlying the coal can be pretty much impermeable.
Yes, usually impressions of the plants that the coal formed from, but ocassionally other things as well, like teeth and shells.
I live in a coal mining region in Australia, the Latrobe Valley. The Powerworks website (http://www.powerworks.com.au) has heaps of info on the formation of the coal, etc, and I found this quote about three screens in:
Click this link for more information, though it may be a little too specific to the coal deposits in my region to be very useful to you.
I work in this industry - primarily in North America. Without exception, coal mining operations here are surface (open pit) mines. As to actual depth of the coal seams, it varies, as does the local topography, but the mine plan generally involves moving the overburden around to expose the coal, and then removing the exposed coal with shovel and truck operations.