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Tabular crystals of grandidierite from the type locality in Madagascar
(repeating unit)
IMA symbolGdd[1]
Strunz classification9.AJ.05
Dana classification54.01.01.01
Crystal systemOrthorhombic
Crystal classDipyramidal
H-M symbol: (2/m 2/m 2/m)
Space groupPbnm
ColorCyan to turquoise; bluish green
Crystal habitTabular
Mohs scale hardness7.5
LusterVitreous, glassy
DiaphaneityTransparent to translucent
Specific gravity2.85 to 3.00
Optical propertiesBiaxial (-)
Refractive index1.583 - 1.639
2V angleMeasured: 24° to 32°, calculated: 32°
Dispersionstrong r < v

Grandidierite is a rare mineral that was first discovered in 1902 in southern Madagascar. The mineral was named in honor of French explorer Alfred Grandidier (1836–1912) who studied the natural history of Madagascar.[2]

A large, faceted grandidierite, a 429.87 carat stone owned by a Filipino collector Benedicto G. Membrere V. GIL Report certificate number STN201811139168.

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).[5]

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, lazulites 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.[6]

See also[edit]


  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ a b Grandidierite: Grandidierite mineral information on Mindat
  3. ^ Grandidierite mineral data on Webmineral
  4. ^ Grandidierite on GemSociety
  5. ^ Ominelite on
  6. ^ "Unusually Large Grandidierite | Gems & Gemology". Retrieved 2020-09-30.