Grandidierite is a very rare collector's gemstone named in honor of the French naturalist and explorer of Madagascar, Alfred Grandidier. Grandidierite is often referred to in the top 10 rarest gemstones in the world and occurs in aluminous boron-rich rocks and in pegmatites. It was first discovered in Madagascar in 1902 and then in small quantities in other areas of the world, but most grandidierite specimens come from Madagascar. The greenish-blue color of grandidierite is caused by the presence of iron. Grandidierite gemstones are usually faceted and sought after by collectors.