Need Help Identifying Rock

[NWTreeOctopus]

My dad found this rock years ago along a creek near Lake Erie. He was never able to figure out what kind of rock it was but I remember him telling all the kids that it was a magic meteorite with gold inside, but if we broke it open an evil leprechaun would get us.

Still to this day, we haven't found anyone who could actually tell us what it might be made of. We did end up breaking it open to see if the inside could help with identifying it. Luckily there was no evil leprechaun.

It feels heavy for its size and has an odd sort of textured shine on the outside. It doesn't attract a magnet at all. The "gold" he was referring to is are the couple of spots where it looks like something pooled then hardened.

 

[jasong]

That's one of those ambiguous, amporphous "whatsits". Even with some basic testing (streak, hardness, density) they can still be a handful of potential rocks/minerals and XRD analysis is often the only way to be certain. It's also clearly been polished by water, naturally. But from the photos it definitely looks like a silicate. It's crystalline. It's fairly fine grained and homogenous. It looks metamorphic to me, in other words it used to be something else. 

I think what you have is a massive form of epidote. Potentially with some quartz in it. See if you can knock a real thin flake off, or put the rock up to the sun/bright light and look at the edges - I'm guessing it's going to be a dark, spinach green. If it is, I can tell you exactly why I think it's a massive form of epidote. It's not very translucent, but with bright enough light and thin enough edge it should show green. 

My 2nd guess would be some kind of quartzite with iron or another metal in it lending dark coloration. My 3rd guess would be some kind of amphibole like hornblende. 4th guess would be magic meteorite with leprechaun inside. 

[NWTreeOctopus]

Hey thanks for taking time to help me out! So I was able to chip a small piece off and put it under the brightest light I had and I see no hints of green. I took a look at it under a cheap handheld microscope and the only colors I can see beyond the brassy discoloration are the off white flecks and shiny black surface, almost metallic/iridescent looking. The brassy color goes from a rusty translucent film where it's thin to a pewter like luster where its thicker. But those are the only colors I see.

I talked to my dad and got some more specifics about where he found it. He said it was along a creek in the bottom of a ravine that used to be a riverbed for glacial waters. Lots of shale bedrock, sand, clay...sandstone further south. Also a large salt mine a few miles away on the lake.

If I wanted to get it tested, should I look for someone local or is it something I should take to the google and send it off somewhere?

[jasong]

If you want it specifically ID'ed, you'll need to send it to a lab that does XRD. Mineral Lab in Denver is one such place, might be one cheaper/closer to you, you'll have to look it up online. A university might do a thin section for you too, they could ID consituent minerals that way too. The local geology around Lake Erie makes almost no difference because much of the cobble in that part of North America came from the Canadian Shield via glaciers, from...who knows where. 

It doesn't look like shale or sandstone to me. Scratch it with a knife. What I really want to know is if it's harder than 4 but less than 5.5, unfortunately there aren't many common objects that you can use for that range. But I still think it's likely massive epidote (unless your photo is playing tricks with light, I can see dark spinach green), however if a knife scratches it, then it definitely isn't that.

Serpentine can look silicified/granular (it's an amphibole too like hornblende), and it can be close to jet black in some cases though it too often shows green under intense light and thin enough flake, but it's usually around a 4 or 4.5 hardness, I've seen up to 5 and as low as 3. 

 

[jasong]

BTW, here is a piece of massive epidote from Wyoming. This one isn't water polished on the outside like your unknown sample is. This is a face cut on a rock saw. 

But it's very similar to what you have. I know this particular piece is epidote (and quartz+limonite, the "gold" bits) because I got it XRD'ed. 4 company geologists didn't believe me but I was positive, so I sent it to a lab on my own dime.  The company paid me back after the results came in. 

It looks pitch black. But flake a thin enough piece off and the very tips of the edges will will be dark spinach green under intense light. A cell phone flashlight isn't sufficient, it needs strong, direct light and a thin edge, I used a gemologist flashlight. 

These massive epidotes also have "imposter" cobbles that look identical via all macroscopic tests, still a mystery to me. They are something else...haven't XRD'ed them yet but they are some partially metamorphosed epidote, quartzite, or amphibole. Metamorphism can leave stuff as a total mishmash. This is why I say these sorts of cobbles can be mysteries forever unless you get a real XRD analysis, even XRF won't help. 

If your sample doesn't scratch with a knife (scratch the outside where it's polished a bit and not rotten), then I still think this is the most likely answer. But I'm not 100%. Maybe something else in the Epidote Group minerals (clinozoisite, etc)? Potentially serpentine/amphibole groups if scratches easily with a knife. 

There is also the somewhat less interesting option that it's just some kind of chert. But it's fracture is what led me away from that at first. 

[Jeff McClendon]

I would go with a hornblende type amphibolite or something similar. Lots of hornblende, amphibole glacier deposited rocks in the Lake Erie area especially with those being found unweathered in the Sudbury/Thetford Canada area north of Lake Erie.