Slate with Pyrite?

[Tonalea]

I bought 80 lbs of slate before learning that the "sparkles" in it were likely pyrite. Here are some photos, any thoughts on suitability for a 75 gall aquarium? Doesn't bubble under vinegar, at least. Take that at what you will, although it's unrelated to pyrite.
I photographed the piece with the most surface sparkles, by the way.

 

[excuzzzeme]

Pyrite (is iron pyrite) aka "fools gold" and is bright yellow. I don't see any yellow (could be me) in those. If I were to guess, I would guess that it is either quartz or mica - both will glisten or reflect light. All three are inert. That doesn't look like slate to me but it could be I guess.

 

[Tonalea]

That's what I was thinking too, about the color of it. It is absolutely silver/whitish without a hint of yellow. There's also no rust around it, as there would be with weathered pyrite, so hopefully I'm in luck. I have a more rock oriented friend (AKA- grad student in a related field) dropping by to check it out in about thirty minutes. I'll let you know what she says!

 

[SubRosa]

That's sandstone. Some of the sand is probably tiny flakes of mica. It will likely slowly crumble over time, but it's inert it's no problem to use.

 

[Tonalea]

Thanks! I guess I just get too paranoid. But I just dropped $80 on fish the other day, the most ever for poor college student me, and certainly didn't want to screw that up!