This appears to be a vintage stick pin featuring a faceted blue navette-shaped glass stone set within a twisted metal border.

This close-up shows the faceted surface and distinct leaf or marquise shape of the deep sapphire-blue stone. The setting consists of an intricate, twisted metal rope-style border that securely frames the gem, a style characteristic of late Victorian and early 20th-century costume jewelry.

The estimated value of a 2.5-inch antique or vintage stick pin with a faceted navette blue glass stone and a twisted border depends heavily on its metal composition: 

• Base Metal / Brass Costume Jewelry: If the metal is a base alloy, brass, or gold-toned plate, its retail value typically ranges from $20 to $45. 

• Gold-Filled / Sterling Silver: If the setting or stem is made of sterling silver or gold-filled metal, the value increases slightly to around $50 to $70. 

• Solid Gold (10K or 14K): If the head or stem tests as solid low-karat gold, even with a paste or glass stone, its value generally sits between $75 to $125 based on the gold content and age