Grandidierite is a rare mineral and gem that was first discovered in 1902 in southern Madagascar. The mineral was named in honor of French explorer Alfred Grandidier. The facet grade stones are very difficult to find. Hardness 7,5 on the moh scale. Collector gemstone.
https://www.nationaljeweler.com/blog/7592-5-things-to-know-about-grandidierite