I'm curious!

Did your mother, grandmother, or spouse collect crystals?

Many humans - perhaps most - keep at least one crystal attached to a finger. Why is that?

In terms of wedding rings, that's not a fundamental human value, but simply because De Beers launched a campaign that still today is a school case for advertising, due to it's ROI.

"In 1938, the diamond cartel De Beers began a marketing campaign that would have a major impact on engagement rings. During the Great Depression of the 1930s, the price of diamonds collapsed.[25] At the same time, market research indicated that engagement rings were going out of style with the younger generation. Before World War II, only 10% of American engagement rings contained a diamond."

https://en.m.wikipedia.org/wiki/Engagement_ring

That refers to diamonds - were there no stones on rings before diamonds, or were there other types?

Regardless of what led to the practice, wearing crystals (or anything) on your finger is still a symbolic expression of the values and beliefs of one's community.

Do marbles count as crystals? A future archeologist can get confused with them.