Brutalist Silver pendant Signed ART

Hi all, first off, is 'brutalist' the right term for this piece? It does appear to be sterling, although it is just marked 'silver' on the back. It is also marked ART inside a shield shaped cartouche. I'm really not sure about the black cabochon; I think it might be glass...thought onyx at first or maybe obsidian? The white spots are reflections. It is about 4" long by 1 1/4" at widest point. I need help with this piece, the search term ART is not helpful. Anyone familiar with this maker? Thanks for looking!!!

 

Yes, it is Brutalist. And a nice chunk of it.
There is another mark below the shield shape, looks like the first part is a 3:


Did you test the stone? It could be obsidian.

 

I think that other mark is just a failed 'silver' stamp like the one above the ART mark. How does one test for obsidian?

 

Obsidian is 6 on the Mohs scale (diamond is 10). So you should have 6 lights on your tester, the same as for instance turquoise.
Onyx is 4.

 

Ah, okay, I don't have one of those testers yet. I guess I'll have to break down and get one. The surface, even though it is very shiny and looks smooth, has tiny pits in it. Also some very fine scratches (tool marks from shaping it maybe?).

 

I'm sorry, I thought you already had one. Did you see this thread:
https://www.antiquers.com/threads/recommendations-for-testing-kits-please.18018/#post-246390
They are not expensive. Otherwise, take it to a jeweler.
Very fine scratches can occur through wear. If they are uniform they could be from a tool.

 

Wonder if we're using the words 'obsidian' & 'onyx' the same way. Obsidian is volcanic glass, brittle, easily fractured, & , according to my mineral guide, 5 - 5.5 on the Moh's scale. Black onyx is chalcedony dyed to that color; same guide puts it at 6.5 - 7 on the scale. (Same guide puts turquoise 5 - 6.) The more durable black onyx is used in jewellery so much more than the fragile obsidian, odds are the stone is the former, particularly if it is opaque seen from the edge.

 

Too many people are confused with the Mexican onyx/travertine with a hardness of 4-5 on the mohs scale which is not real onxy.