925 Sterling Genuine Pearl Makers Marked Dainty Square Black Center Earring

925 Sterling Genuine Pearl Makers Marked Dainty Square w/ Black Center Earrings in excellent vintage condition. 1" x .25". These are stamped with a makers mark that I could not identify with research. The center of each earring is set with what appears to be black stone. I attempted to test them with the presidium gem tester, but the opening is too small to get to the stone. Possibly onyx? The pearls are white with a beautiful luster and green, pink and blue hues. These are s must have for any jewelry lover. Please feel free to ask questions. JW24 yas 23O