Vintage Brutalist Freeform 14k Gold G VS Diamond Turquoise Necklace Pendant / Brooch

This stunning vintage 18k yellow gold brutalist brooch with 5 multicolor semi-precious stones in various cuts. Green tourmaline, pink tourmaline, brown citrine, amethyst, aquamarine on twisty, asymmetrical gold. It is signed what looks like GB 750It also looks like there's another mark that may be 750 as well.  It measures 49.06mm by 39.18mm

(1) Pink tourmaline measuring 9mm by 7mm by 5mm

(1) Brown citrine measuring 9.8mm by 6.6mm by 4.2mm

(1) Amethyst measuring 8mm by 4.9mm

(1) Aquamarine measuring 9.1mm by 6.9mm by 4mm

(1) Green tourmaline measuring 8.3mm by 6mm by 3.8mm

The piece is marked 750 for 18k gold purity and with makers mark "GB" which I believe to be one of Seidengang's Athena markings.

The weight of the pendant is 18.96 grams.