Sir: The Treskilling Yellow stamp is reported to be listed in the Guinness Book of World Records as "the most valuable object of any type by weight, volume and density" (9 November).
This may be true in the realm of manufactured objects. Surely the most valuable substance in the world is from out of this world - Moon rock. It took half a million scientists, technologists and engineers 10 years to bring pieces of rock from the Moon to the Earth at a cost of billions of dollars, consuming the best brains of two superpowers.
Middlesbrough, ClevelandReuse content