The item appears to be an unbranded vintage or antique stick pin featuring an iridescent abalone shell or blister pearl cabochon set in metal.

• Type: Stick pin / lapel pin

• Material: Iridescent abalone or blister pearl with metal backing

• Style: Vintage/Victorian-inspired costume or estate jewelry

The estimated market value for an unbranded, vintage abalone shell or blister pearl stick pin like this typically ranges from $15 to $40

Based on the back of the pin, it is confirmed to be an unmarked costume jewelry piece made from base metal, valuing it at the lower end of the market at $10 to $20