Grandidierite is a rare magnesium aluminum oxide-borosilicate and occurs as a rare accessory mineral in high-temperature, low-pressure metamorphosed aluminous boron-rich rocks such as pegmatites, aplites, and gneisses. The type locality is Cap Andrahomana, Ranopiso Commune, Taolagnaro district (Fort Dauphin), Anosy Region (Fort Dauphin Region), Tulear Province (Toliara), Madagascar, where it occurs as orthorhombic, blue-green, tabular, translucent, vitreous crystals. Grandidierite was named in 1902 for French explorer Alfred Grandidier.
Other notable localities include: Kachebere Hills, Mchinji district, Malawi; Cape Cross area, Swakopmund District, Erongo Region, Namibia; Tizi-Ouchen, Bejaia, Algeria; near Gananoque, Ontario, Canada; Johnsburg, Warren Co., New York, USA; Mt. Amiata and Mt. Cimino, Tuscany, Italy; Vestpolltind, and on Almjotheia, near Moi, Norway; Fiskenaesset, Nuuk, Sermersooq, Greenland Maratakka, Nickerie district, Suriname; and Cuvier Island, New Zealand. It is also known from a number of other minor localities.
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