Glass that has been tumbled and smoothed in the sea washes up on beaches as sea glass, or beach glass. Got these on Etsy, but I replaced the jump ring on the cobalt piece with a silver bail from Rio Grande.
The glass is likely ten or more years old, the cobalt is from a California beach (purchased from Luna Sea Designs), the light blue is from Lake Erie in Ohio (purchased from Beach Glass Memories). Next time I get to a beach I'll be looking for sea glass, it's a little hard in land-locked Missouri. I remember a piece of sea glass I found once on a Suffolk beach, it came from the corner of a bottle and it was the same colour as the light blue pendant. It was a little rough around the edges still, not as smooth as these pieces.