Help with this mineral

[renclod]

Hi, this is my first time posting here.
Please check the graphic attached.
I recently found a rock, or mineral.
My wife spot it and I picked it up.
It looks dark blue, almost black.
When I shine a light trough it, it lits up in a crazy blue.
In normal light it looks opaque, very much so.
When set on top of a led light, it looks clear blue and transparent.
It can scratch ordinary glass (wine bottle).
I was not yet able to measure the density (will do in a couple of days).
I will not show here, for now, the full size. But it is not tiny.
It shows glossy conchoidal fracture marks on about 1/2 surface area.
The other 1/2 surface area is matte, irregular.
Some small crushing areas are blue.
There are 2 intrusions, white - one is shown in the graphic.
So it could be piece of glass ?
Or a sapphire ?
Or something in between ?
Please state your opinion, advice, your thoughts.
Thanks !

 

[JackTrick]

It is always challenging/nigh impossible to identify stones online using photos. Particularly when the photos are so limited.

That said, my guess is slag glass.

 

[whitewave]

I can’t figure out what I’m looking at in the photo, sorry. It’s a bad photo for an ID request, which we really can’t do from photos anyway.

 

[renclod]

Thank you JackTrick and thank you whitewave!
I just did some rough determinations and the specific gravity of this specimen, a mean of 4 measurements, is 2.62.
So I guess it is a glass, probably slag glass like you say.
I had no idea that such a thing (slag glass) exist until I read JackTrick's post above.
This piece is 215 grams (mass) and 70 to 90 cubic cm (volume).
I will not keep this thread busy any longer but just let me show you first some photos.
You may see why I was kind of shocked at the beauty of this chunk of "mineral".

 

[JackTrick]

Yeah! It’s funny how slag glass can be uniquely beautiful