Vintage Art Deco Men's Black Onyx and Diamond Ring

This is a vintage men's signet-style ring, likely dating from the late Art Deco to early Mid-Century period (circa 1930s-1950s). The ring is constructed from a yellow gold alloy, likely 10k or 14k based on the era's common standards. It features a prominent rectangular, flat-top tablet of polished black onyx. Centered within the onyx is a white metal diamond-shaped (lozenge) setting, possibly white gold or platinum, house a single small round-cut diamond. The setting is secured by four decorative gold prongs or 'tabs' at the midpoints of the rectangular onyx face. The shoulders of the ring exhibit period-appropriate geometric engravings and stepped detailing, characteristic of Art Deco design. Regarding condition, the ring shows significant signs of wear consistent with age; there are visible surface scratches on the gold shank and the onyx tablet. The gold appears to have a slight rosy patina in recessed areas. Small nicks are visible along the edges of the onyx. No specific maker's mark is visible from this angle, but the craftsmanship suggests a mass-produced yet high-quality commercial piece from the mid-20th century.