This is a gold ring that has been affected by exposure to chlorine.
Chlorine causes a chemical reaction to take place between the chlorine and the alloy metals in gold jewelry and certain jewelry items actually disintegrate over time.
If a ring is cleaned with chlorine bleach, the ring may turn black and develop small hairline cracks, even a few hours later.
Research has shown that when a 14k white gold ring is placed in common household chlorine bleach for 36 hours, the end result was complete disintegration.
This contamination is often irreversible.