Grandidierite is a rare mineral that was first discovered in 1902 in southern

Madagascar Madagascar, officially the Republic of Madagascar, is an island country that includes the island of Madagascar and numerous smaller peripheral islands. Lying off the southeastern coast of Africa, it is the world's List of islands by area, f ...

. The mineral was named in honor of French explorer

Alfred Grandidier Alfred Grandidier (20 December 1836 – 13 September 1921) was a French natural history, naturalist and List of explorers, explorer. From a very wealthy family, at the age of 20, he and his brother, Ernest Grandidier (1833–1912), undertook a ...

(1836–1912) who studied the natural history of Madagascar. Grandidierites appear bluer in color the more iron (Fe) they contain. A recently discovered gemstone, blue ominelite, is the Fe-analogue (Fe, Mg) to grandidierite (Mg, Fe). Grandidierites display strong trichroic pleochroism. That means that it can show three different colors depending on the viewing angle: dark blue-green, colorless (sometimes a very light yellow), or dark green. While trichroism can usually help distinguish grandidierites from other gems,

lazulite Lazulite or ''Azure spar'Krivovichev V. G.'' Mineralogical glossary. Scientific editor A. G. Bulakh. — St.Petersburg: St.Petersburg Univ. Publ. House. 2009. — 556 p. ''(in Russian)'' is a transparent to semi-opaque, blue mineral that is ...

s can occur with blue-green colors and show colorless/blue/dark blue pleochroism. Nevertheless, lazulites have somewhat higher refractive indices and specific gravity. Grandidierites also have greater hardness, with a 7.5 on the Mohs scale. Large transparent faceted grandidierite specimens are extremely rare. The largest cut specimen currently known to the GIA weighs in at 763.5 carats.

References

Orthorhombic minerals Minerals in space group 62 Nesosilicates Gemstones {{silicate-mineral-stub

See also

References