Nauruit
Nauruit is the historical name for a fluorine-containing phosphorite that was found exclusively on the eponymous Pacific island of Nauru .
Nauruit was found in the form of thin, hard and brittle bark on the dolomite of the corals , but also on ordinary phosphate ; sometimes it was also a binder between the phosphate grains. The chemical composition is the same as for other phosphates, but with 1.9 percent fluorine content .
See also: History of Naurus