Our group has been walking old rail lines of an old mill (Lyons Cypress/Garyville Northern)
and we are finding a few inches of coal, some fine and some as big as baseballs,this was not an isolated finding, we found in for a long way, non stop and on different spurs fairly consistent.
We are looking at putting in a few miles of tracks after leveling the old right of way.
What could have been the reason we are finding coal, for miles? My thought for now is when the rails were sold to the Japanese for some reason it was back-filled with left over coal from the steam powered mill.
We had a group of train buffs with many years of Rail Road history behind them and they were stumped.

Thanks,
Colin

Is it cinder ballast?

Many railroads in my area of the northeast used cinders and clinkers left over from the burning of coal for ballast as it was cheap and plentiful. If the mill in question burned coal, they probably had plenty of ash and cinders to use for ballast.

Just my 2 cents

In the late 1800s, the Philadelphia & Reading RR was so poor that they couldn't afford to buy dirt to fill in rotting wooden trestles. So, they used something cheaper - fine particles of coal that were too small to use in hand fired furnaces. A layer of expensive dirt was put on top for fire protection. In the late 1970s, the modern owners of the company made a fortune selling those fines from under abandoned branches to power plants with automatic stokers that were made to blow light weight particles into their furnaces.

It is mostly fine particles but we can easily dig up large chunks that are coal.
you can see the layers in it. Someone grabbed a few chunks to get it tested. Maybe it was cinders that compressed to look like coal.

Hi
On the Boston & Albany Milford branch located in Massachusetts, the railroad always used the best ballast they could find, at the cheapest price. The type of ballast was always Cinders from the locomotives.
Once it is packed on the roadbed, it was just like concrete, it wouldn't move, the only time you saw stone ballast was if they had a bad drainage problem.
The Milford branch ran from Framingham, Mass to Milford, Mass a distance of 12 miles.

Cinders, absolutely. Some bits of coal intermingled, sure. But coal in quantity? I've never heard of that so we await the results of your test. Coal, especially old coal that has been exposed to the elements and no longer has much of the volatiles it once did, may not ignite easily. But get a good, very hot charcoal fire going in your barbecue and then toss your suspect lumps into it and see if it ignites.