Featured Silver Brooch from Mexico - Question about stone used, era & designer

Onyx is a banded variety of the silicate mineralchalcedony. Agate and onyx are both varieties of layered chalcedony that differ only in the form of the bands: agate has curved bands and onyx has parallel bands. The colors of its bands range from white to almost every color (save some shades, such as purple or blue).

Brazilian green onyx was often used as plinths for art deco sculptures created in the 1920s and 1930s. The German sculptor Ferdinand Preiss used Brazilian green onyx for the base on the majority of his chryselephantine sculptures.[17] Green onyx was also used for trays and pin dishes – produced mainly in Austria – often with small bronze animal figures attached.

But what do i know.....

 

Thanks all! Great help as usual. I'm working on the eBay write up now. BTW, our eBay activity the last few weeks has been awful. Offers, feedback, orders, messages - all down in the dumps. The fall buying season hasn't kicked in yet.