Looks like the stone is about to fall out of the bezel.
Looks like the "stone" is some type of glass.
Lavin history............. https://www.worthpoint.com/dictionary/p/jewelry/-american/lanvin-jewelry Most modern Lavin jewelry is made in Italy.
There is no engraving... the bail was stamped and the lettering on the base was in the mold casting of the whole piece.
Looks like a doublet,black stone base with a thin opal top.
You might be surprised at the number bench jewelers who will saw through maker's marks when doing resizing and repairs.
look here..... https://www.art-amerindien.com/hallmarks/
Shine a light through it and see what it looks like.May be a type of rutilated quartz........
Made in New Zealand,possible jade.
Can you get a side photo of the stone or do you know what it is.
It looks a bit like red moss agate..... https://stoneworkcabochons.com/products/copy-of-amethyst-sage-agate-cabochon
It's not a mark it's a factory defect.
Looks like it was cast,air bubbles on all surfaces.
Doesn't look like amazonite.
They are rhodolite garnets from the Cowee Valley North Carolina area.
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