Dated from the early 20th C. A lovely old European 800 silver pendant with a stunning red rectangular step cut red paste stone. 
I am in love with the electric red colour of this stone, a really superb example of the quality of paste
(lead glass coloured by selenium) from this time.
 
Stamped 800 on the back. 
800 silver is an alloy of silver that is 800 parts silver and 200 parts other metals common for Europe around that time.
 
Believed to have originated in Austria.