Djúpalónsperlur

The pebbles at Djúpalónssandur are called Djúpalóns pearls, they are used for making jewelry. The outer layer is of volcanic glass whereas the inner part is fully crystallized (Benmoreite). That much I gathered from volcanologist Haraldur Sigurðsson's blog (it's in Icelandic and online translators make rather a hash of the language...)