Odd stone?

[Gimlis Ghost]

A few years back I spotted an unusual dark brown stone near the railroad tracks.
It was already broken and the raw end looked much like a broken chocolate cookie.
I could see light glinting off near microscopic crystal throughout the stone.
The exterior was smoothed by centuries of water flow.
Finding a nearly flat area I stroked a pocket knife blade across it and it left a thin smear of steel like pencil lead. One light stroke on each side of the edge and the not quite dull blade was now sharp as a well stropped razor. Only thing like it I've tried was a leather tool sharpening "Rubiyat stone" ,a synthetic gem stone.

Any idea what this stone might be?

[Eric Krewson]

My guess would be iron pyrite, metallic inside and often found with coal. If a coal fired train ever ran the tracks where you found it that would be the source.

We separated tons of the stuff from the coal as it fed into our coal pulverizers at the power plant.

[Gimlis Ghost]

My guess would be iron pyrite, metallic inside and often found with coal. If a coal fired train ever ran the tracks where you found it that would be the source.

We separated tons of the stuff from the coal as it fed into our coal pulverizers at the power plant.

I think you are probably correct.
I'd only seen Pyrite in the crystal Fool's Gold form but I did a search for Brown Iron Pyrite and found some polished jewelry stones that look very much like this smooth stream washed stone.
The Brown Pyrite stones come in many forms .

I wonder if its ever been a commonly used whetstone material.

[Eric Krewson]

Looking back I should have stockpiled some of this "fools gold", pieces were often as big as my fist. I know now that people with matchlock rifles pay exorbitant prices for iron pyrite to use in their locks, ridiculous prices.

I would suspect that pieces of this stuff about the size of 50 cent piece and marked on eBay as "fools gold" would sell like hotcakes to the curious.

I just checked eBay, not as valuable as I thought but 10 OZ goes for $14.95, no too bad if you have tons at your disposal.

[Gimlis Ghost]

Looking back I should have stockpiled some of this "fools gold", pieces were often as big as my fist. I know now that people with matchlock rifles pay exorbitant prices for iron pyrite to use in their locks, ridiculous prices.

I'll try some experiments on striking sparks from steel later. Could be a good substitute for flint in primitive fire making.