In 2013, at the suggestion of oceanographer Charles Moore, geologist Patricia Corcoran and artist Kelly Jazvac began a research project on a new type of stone they have since described as 'Plastiglomerate.' The stone consists of a mix of molten plastic debris and beach sediment, including sand, wood, and rock. A co-authored manuscript of their findings, and related press, can be found here:
Photo credit Jeff Elstone