Mod ring bought in The Hague, NL

[TackyAki]

Hi everyone! I'd love to identify this ring. I bought it in a little antique shop in The Haag, NL, last winter for €10

I'm unsure of the gem, probably fake, but its totally unscratched, whereas the black (glass? Onyx?) has some faint hairlines.

Was really tarnished and haggard when I bought it. Polished real nicely.

I can't see the mark any clearer than I got a photo of. RJ, RI, RU??

Curious to find out more!

-Aki