Can someone explain this and what it is? Broke it open it was empty, looks like pyrite cube was in there but dissolved? Found in PA coal mine
13 comments · 100% upvoted · source · other discussions
comments
[deleted]
[deleted]
Damn that's probably one of the top 5 coolest rocks I've seen here.
Ithaca_Lapidary
I was thinking possibly fluorite.
You're on the right track. That's an epimorph, a mineral cast of a mineral, where the original mineral dissolved away. In this case it was probably calcite.
[deleted] 10 points · Aug 2019
That’s really interesting! I’m pretty casual on the rock collecting world, didn’t even know this was possible!
spartout 2 points · Aug 2019
It was definitely pyrite rather than calcite. The shape matches the cubic shape of pyrite perfectly while i cant see any rhombic shapes which would indicate calcite.
[deleted] 3 points · Aug 2019
Oh, it isn't calcite then, but it definitely isn't pyrite. Pyrite doesn't dissolve, so it would have to melt into acid, and I don't see any evidence of that happening, plus pennsylvania doesn't have perfect cubes that would cause something like this. Probably fluorite then.
DigDigDig11 [OP] 2 points · Aug 2019
I've found plenty of perfect pyrite cubes here: https://youtu.be/2L6oRRrXJt0
spartout 0 points · Aug 2019
Pyrite indeed doesnt dissolve at neutral pH conditions, however this doesn't eliminate it as an possibility, It doesnt take a strong acid at all to dissolve it given time which this has had plenty of .
DigDigDig11 [OP] 0 points · Aug 2019
There's loads of pyrite in this coal mine, but not in spherical rocks. I've never found calcite there....just quartz crystals.
spartout 0 points · Aug 2019
Thats quite the oddity, can you post a photo of the pyrite from the mine? Also does the mine have groundwater flowing? Because pyrite reacts with water forming iron hydroxides and sulfuric acid so if it has a lot of water that might explain how this piece dissolved away.
DigDigDig11 [OP] 2 points · Aug 2019
Not really visibly flowing water, but the pyrite level is directly above the coal seam, and I find very colorful "peacock coal" there, which I believe occurs when water hits the pyrite level and seeps sulfides(?) into the coal.
DigDigDig11 [OP] 1 points · Aug 2019
I posted a video(slideshow) of pyrites I found in the same mine above in the comments.
briancane 1 points · Aug 2019
Yeah that yellowish staining could very well be what’s remaining of the pyrite turned into an acid