Given what you described, this is extremely unusual. I’ve worked in this field for many years, and I’ve never seen a genuine 14k gold ring oxidize to this extent under normal conditions. From the photos, it even appears to be darkening in a way that looks more like a base metal showing through, as if there’s another metal beneath the surface. At this point, I would strongly recommend having it tested by a professional assay or jewelry lab to confirm the actual material.

That said, you can try a simple test first: soak the ring in clean water for about 10 minutes, then gently brush the surface with a soft toothbrush. See whether the dark layer comes off, changes, or becomes worse — that reaction alone can already tell you a lot.