I would say that they are an [**odd**][1] **pair of earrings**.

As one of the definitions for odd given in Collins Dictionary:

>6. adjective
>
>You say that two things are odd when they do not belong to the same set or pair.
>
>"I'm wearing odd socks today by the way."

[1]: https://www.collinsdictionary.com/dictionary/english/odd