Gatsby Jewellery Ltd has dated this piece to the 1910s.
The back of the brooch is in 18k yellow gold with a yellow gold pin.

Accompanied by an independent jewellery report from IGR (#30309568).
Cut – Cushion cut paste and rose cut diamonds.
Colour – The diamonds range from F to G.
Clarity – The diamonds are SI1 to SI2.
Carat – The green paste is approximately 8.70 carat, with approximately 0.62 carat of diamonds.
Circa – 1910.
Measurements – The green paste, including the rubover platinum around it, is 15.2 x 11.4mm. The brooch is 34.6 x 26.5mm
Metal – Platinum and 18k yellow gold. Tested.
Gatsby Jewellery Ltd has dated this piece to the 1910s.
Gatsby jewellery are a husband and wife team who have years of knowledge and experience in dealing in fine antique jewellery.
You can view the stock and full dealer information on the Gatsby Jewellery Ltd Profile Page