This is a fantastic Georgian piece. It tests around 9k gold which is common in Europe. There is about 1 CT of rose cut diamonds, could be more but it's hard to estimate weight on rose cut diamonds. It weighs 15.9 grams. There is something special about this brooch.
I'm not sure if it would be considered. En Tremblant or something similar. I have seen several similar brooches go into the thousands. Antique Georgian Era Rose Diamond & Gold Brooch Pin - Arrow Floral Crescent Moon - YouTube.The item "Antique Georgian Era Rose Diamond & Gold Brooch Pin Arrow Floral Crescent Moon" is in sale since Friday, June 29, 2018. This item is in the category "Jewelry & Watches\Vintage & Antique Jewelry\Fine\Art Nouveau/Art Deco 1895-1935\Pins, Brooches". The seller is "worldpawnexchange" and is located in North Bend, Oregon. This item can be shipped to United States, Canada, United Kingdom, Denmark, Romania, Slovakia, Bulgaria, Czech republic, Finland, Hungary, Latvia, Lithuania, Malta, Estonia, Australia, Greece, Portugal, Cyprus, Slovenia, Japan, Sweden, South Korea, Indonesia, Taiwan, South africa, Thailand, Belgium, France, Hong Kong, Ireland, Netherlands, Poland, Spain, Italy, Germany, Austria, Israel, Mexico, New Zealand, Singapore, Norway, Saudi arabia, United arab emirates, Qatar, Kuwait, Bahrain, Croatia, Malaysia, Brazil, Colombia.