You're both very close.
Is it indeed a stone, used for polishing, but not for gunsmithing or gems.
It's fairly soft (as stones go), if that helps any.
See if you can guess the material, that'll be close enough for a win.

Jade stone.

http://www.ebay.com/itm/10000-Grit-Knife-Razor-Sharpener-Super-Fine-Stone-Whetstone-Oilstone-Polishing/251583204867?_trksid=p2054897.c100204.m3164&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20140407115239%26meid%3D33be50fe4c214123a551cd904810459c%26pid%3D100204%26rk%3D3%26rkt%3D29%26mehot%3Dpp%26sd%3D251805652700

I've never heard of using Jade as a stone.  And it's small size made me think it wasn't for knives.  The only other small stones I've seen like that are stone-files for gunsmithing...


Except, you said it's a very soft stone and the Jade being labelled as both 10,000 grit and super fine would make it an extremely hard stone...

Used for sharpening knives or polishing the sharpening?

Looks like soapstone?! ... pain in the butt and fiddly/powdery crap! Lol

Fish hook sharpener

Watcher has the right product, and Yama has the correct usage.

It's solid jade, used for final polishing on the edge of my forged knives.
Jade is very soft, as stones go. The "10k grit" is pretty much made up, and has nothing to do with the hardness of the stone.
All I know is that it puts a finer edge than my 6k grit diamond lapping compound, so maybe it's pretty close...?

Anyway, congrats to Watcher, since he even found an eBay link that looks similar to the one I bought it from. lol

Watcher, PLEASE post something, I'm out of ideas.

I can put a edge on a knife that will shave hair but I've got to get one of those. Are they just for forged blades? Never knew those existed.

I feel like I've used one of these before, but I had a busy day and this was readily available.

No idea. ... but just for fun. .. Kryten's left nipple nut?

Small hole on one face, some manner of flow regulator? 

NOS nozzle/fogger

So close yet so far.

Direction is right, application is wrong.

Sintered inline filter?

Not a filter, regulator, or nozzle.  It might be installed in a regulator, though.

Burst disc?

 

Oh goodie, I win!

Wait, now I have to find something to post....dang it! 

Ok, give this one a try...
For reference, it's about 2" long.


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Hang on. . Not dispute win. . But wth is a burst disc?

And your 2" long widget there Mojo. .. you find that in your pants? :p bahahaha