Blåvinge is a small, kind of vintage blue coloured butterfly (Polyommatini). In Sweden you will often see these in dry places and around ditches and pastures.
The colour of these earrings reminded me of the butterflies, with the sometimes dirty or smoky blue colour. I do think the crystals are actually glass, but they are pretty anyway! However they have a coating of metallic blue and attached to bronze coloured metal. The hooks are off course nickel free.