Randomly, a person who was a student at my high school posted a picture of a class ring that is up for auction on a local site in the area (Idaho). It is a woman's class ring from 1967, the year I graduated. Much discussion ensued. It looked like the initials might be KM but we weren't sure. One of my classmates from that year posted that she had lost her ring years ago at a lake. However, she was fairly certain that the stone was a turquoise color. The stone in this ring looks black.

I have confirmed with the auction place that the initials are KM, so that narrows this down to her or one other classmate with the same initials. Does anyone have any insight as to what might happen to a stone in a ring if it was in water for maybe years? Several of my classmates are willing to chip in to bid on this ring and return it to her if we can be pretty sure it's hers. But, the stone color is a puzzlement.

Interesting question. Does "turquoise color" mean actual turquoise or something like an aquamarine, tourmaline, etc.?

Here is one article on how turquoise stones can darken with exposure to water or oil:

https://tskies.com/does-turquoise-change-color/

The other turquoise-colored stones appear to be stable to water, i.e. aquamarine, tourmaline, and possibly topaz or opal. They are, however sensitive to heat or fracture.

http://www.studleysjewellers.co.uk/gemstone-guide/

You might ask your classmate about her ring size. That might narrow it down.

That was very informative, Summer. The ring has her initials and is the right size. However, the auction person said he is certain the stone is black and was never a different color. So, I let the other classmates know that I won't be bidding on it and the mystery is just that. I guess it is possible that the classmate who lost the ring is mis-remembering the color. It was just a little burst of excitement that we might be able to reunite a long lost class ring to a beloved classmate.

The stone if it was turquoise might have fallen out in the intervening years, and been lost. Maybe it was replaced with a different stone, in this instance with one that is black as a replacement stone. Is the stone Onyx? Or does the seller know what kind of stone it is? Turquoise could be a deep blue or green? But not black.