Sterling silver letter opener

Does anyone know anything about this letter opener? I have searched and searched and cannot find anything like it. It was very tarnished when I got it but I have gotten it to shine up pretty nice. It has some type of green stone/marble encased in the handle.

There are a couple of stamps on it. At the bottom of the silver there is a stamp that says "Silver" and a stamp below it that says "Sterling". In the middle right before the blade starts there is a stamp that says "Mexico" and a stamp below it that says "Silver". Then on the front and back there are 3 upside down V/arrow looking shapes. Other than that I couldn't find any other marks. However, it seems like an old piece so they may have disappeared.

 

It's a nice piece!
You've pretty much answered your own questions.
Mexico, sterling, vintage. I believe the stone is malachite. Too bad about the big dent.
Information about hallmarks here:
http://www.silvercollection.it/mexicosilvermarks.html

 

The stone in the handle looks like dyed Mexican onyx/travertine.

 

Thank you for the info! Any ideas on a time frame it would have been made or a possible maker?

 

Could you show us the actual marks? If there is no maker's mark it is impossible to find the maker, but the type of mark and lettering are usually an indication of the period. The V shapes are just decoration, no silvermarks.