Planet Money had a segment about the rocks-as-currency island:. Segment: http://www.npr.org/blogs/money/2011/02/15/131934618/the-island-of-stone-money http://w

Planet Money had a segment about the rocks-as-currency island:. Segment: http://www.npr.org/blogs/money/2011/02/15/131934618/the-island-of-stone-money http://www.npr.org/blogs/money/2011/02/15/131934618/the-isla... Entire podcast (also discusses the currency test, IIRC): http://www.npr.org/blogs/money/2011/02/15/131963928/the-friday-podcast-a-giant-stone-coin-at-the-bottom-of-the-sea http://www.npr.org/blogs/money/2011/02/15/131963928/the-frid... Very interesting.