These are vintage Mexican sterling silver and "Alpaca" leaf screwback earrings, likely featuring an abalone inlay on the front, dating from the mid-20th century (circa 1940s–1950s). 

• Hallmarks: Stamped "STERLING" on the leaf base and "ALPACA" on the screwback mechanism (Alpaca refers to a silver-colored nickel alloy commonly used in vintage Mexican silver jewelry findings)

The estimated market value for this pair of vintage Mexican abalone and sterling silver leaf earrings typically ranges from $25 to $55