Allan asked;

"Does pyrite also form in coal beds?"

Definitely, yes. It can be quite abundant in many coal. In fact,
it is a major source of sulfur dioxide created by the burning
of high-sulfur coals. It also is the source of sulfuric acid in
water draining from the abandoned coal mines. For example, this
problem is discussed in a Knasa Geological Survey web page,
"Coal Mining in Kansas" at [www.kgs.ku.edu].

In this article,it is stated:

""Gob piles, the piles of discarded coal
waste and fractured rock, are another
problem associated with abandoned coal
mines. These gob piles contain iron
pyrite, sometimes called fool's gold
because of its yellow metallic luster.
Pyrite is iron sulfide; when exposed
to water and oxygen, pyrite undergoes
a chemical reaction that produces sulfuric
acid, iron oxides, and hydroxides. The
iron oxides and hydroxides, similar to
commun rust, tint these gob piles red.
Sulfuric acid, however, pollutes both the
water and soil around the mines."

and another article, "AMD - What is Abandoned Mine Drainage or
Acid Mine Drainage?" at [www.scrip.pa-conservation.org]

Another of many such discussions can also be found in the Illinois
State Geological Survey General Geology FAQ, "Reducing the sulfur
content in coal before burning" at [www.isgs.uiuc.edu].

Yours,

Paul H.

"The past is never dead. It's not even past."
William Faulkner, Act 1, Scene III, Requiem for a Nun (1951)