How Old is This Brooch and Is this Glass or Amethyst Stone

Good afternoon everyone. I was out garage hopping and came across this lovely brooch for $3. It measures 3 inches by 2 inches and has the "C" hook with a long pin. I tried to do some research on-line and the stone does scratch glass and tile. I'm wondering if this is a 19th century to early 20th century brooch and if the stone is a real amethyst. Also there appears to be a hallmark on the back which I can't read. Is the metal silver or silver plated? Anything you can tell me about this brooch , would be gratefully appreciated. Is there any value to it? Thank you so much ahead of your answers for your time and interest.
Karen S

 

My first guess would be Czech brass and glass, 1920s into the 1930s.

 

Thank you evelyb30. Do you think there is any value?

 

Some, but not crazy high. How much depends on when and where it's sold.

 

I was planning on selling it on my Etsy vintage jewelry shop (required age at least 20 years by Etsy). Is it OK to ask what you recommend pricing it at? (I don't know if that's allowed in the forum!. So sorry if it isn't allowed)

 

I don't sell on Etsy or buy there, so it might be best to do a quick and dirty search over there.

 

I checked at Etsy and a Czech 1920-30s brass and purple glass brooch this size sales for about $45 to $55. Does that sound reasonable to you?

 

Better than I'd get for it, but Etsy is about retail for some things.

 

Thank you evelyb30 for all you help and comments. I listed it at the low end.
Karen

 

Fingers crossed!