Grandidierite Value, Price, and Jewelry Information


grandidierite cabochon
5.12-ct grandidierite, medium dark bluish green, oval cabochon, 10.7 x 9.3 mm, Madagascar. © The Gem Trader. Used with permission.

A rather rare mineral, lovely blue-green grandidierite is seldom seen in gem or jewelry collections. Translucent material is sometimes cut into cabochons. Faceted pieces are very rare, but recent discoveries of transparent material may bring more to the market.

Grandidierite Value

The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.

Grandidierite Information

DataValue
NameGrandidierite
Crystallography Orthorhombic. Crystals elongated and not well formed; massive.
Colors Blue-green.
Luster Vitreous
Fracture Uneven
Hardness 7.5
Specific Gravity 2.85-3.0
Birefringence 0.039
Cleavage Perfect 1 direction, good 1 direction
Dispersion Very strong.
Luminescence None.
Transparency Gem material is translucent to transparent. Generally opaque.
Absorption Spectrum Absorption line at 479 nm.
Formula(Mg,Fe)Al3BSiO9.
Pleochroism Strong: dark blue-green/colorless/ dark green.
Optics a = 1.583-1.602;  β = 1.618-1.636; γ = 1.622-1.639. Biaxial (-), 2= 30°.
EtymologyAfter Alfred Grandidier, a French explorer who described the natural history and geography of Madagascar.
OccurrenceGenerally in pegmatites.
Inclusions Crystals (chlorapatite, monazite, zircon), two phase inclusions (vapor/liquid), needle-like channels, parallel growth planes.
grandidierite crystals
Grandidierites in a cluster of crystals, from Cap Andrahomana, Ranopiso Department, Anosy (Fort Dauphin) Region, Tuloar Province, Madagascar. © Rob Lavinsky, www.iRocks.com. Used with permission.

Comments

Grandidierite has a hardness of 7.5, which makes it very resistant to scratching and ideal for jewelry use. However, it also has perfect and good cleavage in two directions, which makes it challenging to cut. Of course, its scarcity has also made this a relatively little known gemstone.

Since its discovery in 1902, most gem-quality grandidierite has been translucent. Cabochons cut from this material look very attractive and may even appear jade-like. Recent discoveries of transparent material in Sri Lanka (around 2000) and a new deposit in Madagascar (2014) have resulted in beautiful, faceted gemstones.

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).

Identifying Characteristics

Grandidierites display strong trichroic pleochroism. That means they can show three different colors depending on the viewing angle: dark blue-green, colorless (sometimes 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. They also appear cabbed and, more rarely, faceted. Nevertheless, lazulites have somewhat higher refractive indices (RI) and specific gravity (SG). Grandidierites also have greater hardness. Keep in mind that scratch tests for hardness should only be used as a last resort to identify rough. Don’t conduct this test on a finished gemstone.

Grandidierites from Madagascar may have following properties (on the lower end of the typical range):

  • RI: = 1.583; γ = 1.622.
  • SG: 2.85.
grandidierite - 2.43 cts
Faceted grandidierite, 2.43-ct, Madagascar. Photo by DonGuenne. Licensed under CC By-SA 3.0.

Synthetics

Scientists have synthesized grandidierites for projects such as research into recently discovered ominelite as well as the occurrence of werdingite in pegmatites. However, there is no known use for this synthetic material in jewelry. (Perhaps this will change if grandidierites become better known).

Enhancements

No known treatments.

Sources

For many years, Cap Andrahomana in southern Madagascar, the type locality, was the only well-known source of gem-quality material. A new find in Tranomaro, also near Cap Andrahomana, has produced transparent, gem-quality grandidierites.

faceted grandidierite - Tranomaro, Madagascar
Faceted natural grandidierite, Tranomaro, Madagascar. Photo by American-thai. Licensed under CC By-SA 4.0.

The Kolonne region of Sri Lanka has also produced gem-quality material.

Other sources include the following:

  • United States: New York, Wyoming.
  • Algeria; Antarctica; Czech Republic; Italy; India; Malawi; Repanga Island, New Zealand; Norway; Slovakia; Suriname.

Stone Sizes

As cabochons, translucent grandidierites can range from 1 to 10 carats and up to about 1 inch in size. Much material is generally opaque.

Care

Grandidierites have the durability to do well in any jewelry setting. However, some stones may have inclusions of crystals of other gem materials. Because of their cleavage and “brittle” tenacity, they may also have increased susceptibility to blows and chipping. For these reasons, avoid mechanical cleaning systems. Instead, use a soft brush, mild detergent, and warm water. Consult our gemstone jewelry cleaning guide for more recommendations.

1.1-ct grandidierite - Madagascar
Grandidierite: Madagascar (1.1). Photo © Joel E. Arem, PhD, FGA. Used with permission.