Large cocktail ring with a rectangular blue-green gemstone

This is a statement cocktail ring featuring a very large, emerald-cut or rectangular step-cut blue-green stone set in a yellow metal mounting. The stone exhibits a deep teal or greenish-blue coloration with visible internal inclusions, surface scratches, and facet wear typical of vintage costume jewelry or a softer colored gemstone such as tourmaline, topaz, or synthetic spinel. The setting utilizes four simple, rounded prongs that secure the corners of the stone, attached to a slender, polished yellow metal band. There are no maker's marks, hallmarks, or stamps visible in the provided photograph, making the exact metal purity and stone composition unverified. The overall aesthetic suggests a mid-20th-century fashion piece, though without physical inspection or testing, the materials remain unidentified. Condition shows moderate surface wear on the table facet of the stone, consistent with age and prior use.

Based on what I can see in the photograph, this item appears to be a mid-20th-century fashion cocktail ring featuring a large rectangular step-cut blue-green stone set in a yellow metal mounting. I can't verify the exact composition of the metal or the gemstone from a photo alone; the stone exhibits visible internal inclusions and surface wear that could suggest a softer colored gemstone like tourmaline or synthetic spinel, or potentially quality vintage costume glass. I would need physical inspection and gemological testing to confirm these materials. There are no visible maker's marks or hallmarks in the image, leaving the exact origin unverified. My value estimate of $150 to $300 assumes the piece is crafted from precious metals and a genuine semi-precious stone. General market demand for vintage statement cocktail rings of this aesthetic is moderate among collectors of mid-century fashion jewelry. If physical testing reveals the piece to be modern costume jewelry utilizing base metals and synthetic glass or plastic, the value would likely decrease to the $30-$75 range. To establish a more precise valuation and confirm authenticity, I would recommend an in-person examination by a qualified gemologist, hallmark verification if any stamps emerge upon microscopic inspection, and professional metal testing.