This appears to be an antique gold solitaire diamond stickpin featuring a sparkling round stone set in a delicate multi-prong basket mounting

If it is Gold-Filled or Base Metal: Antique pins made with gold-filled metal or plated brass generally sell for $20 – $50

If it is Faux (Paste or Glass): It was very common in the Victorian and Edwardian eras to use "paste" (leaded glass) or white sapphires to mimic diamonds. If it is paste, the value will sit under $40 unless the metal itself is high-karat gold.