Grandidierite
| Grandidierite | ||
|---|---|---|
2V angle Measured: 24° to 32°, calculated: 32° | | |
| Dispersion | strong r < v | |
| References | [2][3][4] | |
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]
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
References
- S2CID 235729616.
- ^ a b Grandidierite: Grandidierite mineral information on Mindat
- ^ Grandidierite mineral data on Webmineral
- ^ Grandidierite on GemSociety
- ^ Ominelite on Mindat.org
- ^ "Unusually Large Grandidierite | Gems & Gemology". www.gia.edu. Retrieved 2020-09-30.
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