How did it get there? And much more important where did the metal come from?
The blue “Skystones” are another mystery. A legend says: The part of the sky in which the Nomoli lived turned to stone. It splintered and fell to Earth as pieces of rock. Scientists found traces of iridium in the “Skystones”. Iridium is one of the least abundant elements in the Earth’s crust, having an average mass fraction of 0.001 ppm in crustal rock.
It is thought that the overall concentration of iridium on Earth is much higher than what is observed in crustal rocks, but because of the density and siderophilic (“iron-loving”) character of iridium, it descended below the crust and into the Earth’s core when the planet was still molten.
Iridium is found in meteorites with an abundance much higher than its average abundance in the Earth’s crust. For this reason the unusually high abundance of iridium in the clay layer at the Cretaceous–Paleogene boundary gave rise to the Alvarez hypothesis that the impact of a massive extraterrestrial object caused the extinction of dinosaurs and many other species 65 million years ago.
When searching for diamonds in West African Sierra Leone, local people made unexpected finds: They repeatedly came across 40 to 70 cm tall stone sculptures.
The origin of these Nomoli is uncertain and some were discovered at depths of 50 metres.