The geometrics of this lovely stick pin suggest to me that it is an art nouveau/deco transitional piece, circa 1920. The pin head is 1/2 inch high and a little over 3/8 inches wide and holds a rectangular amethyst paste stone. The total height of the piece is a little over 2 and 3/8 inches. It weighs 1.0 grams.
Marked "10K" on the pin stem, under the head of the piece.
10K Gold Amethyst Paste Stick Pin Art Nouveau Deco Transitional