5 Things to Know About … Grandidierite

When I was in Tucson, the team at Omi Gems’ booth treated me to something special: a viewing of not one but six grandidierite gems.

I had heard of the gemstone before but had never seen one in person. As it turns out, not many people have. They’re rare, and let me tell you, they’re gorgeous.

Grandidierite is bluish-green to greenish-blue, with the blue component increasing with the iron content, according to the GIA.

It’s a 7.5 on the Mohs scale, making it suitable for use in jewelry (when available), but according to the International Gem Society, it is difficult to cut because it has good cleavage in two directions.

It also displays trichroic pleochroism, meaning it can show three different colors depending on the angle at which it’s viewed: dark blue-green, pale yellow or colorless, or dark green.

In honor of the stone I was excited to see and learn about in Tucson, here are five things to know about grandidierite.

1. It was first discovered in Madagascar.

French mineralogist Alfred Lacroix found the first reported samples of grandidierite in 1902.

He discovered the gemstone at the cliffs of Andrahomana in southern Madagascar, according to the GIA.

2. It was named for someone. 

As is the case with a few other minerals ending in “ite,” grandidierite was named after a person. 

Lacroix christened the mineral “grandidierite” in honor of another Alfred: French explorer and naturalist Alfred Grandidier (1836-1912), who was the first explorer to describe Madagascar in detail, according to the Cambridge History of Africa. 

He devoted his life to gathering information for his massive “Histoire physique, naturelle et politique de Madagascar,” which was 38 volumes long. 

3. It has since been found elsewhere.

In addition to Madagascar, GIA said other reported sources of the mineral include New Zealand, Norway, Suriname, Algeria, Italy, Malawi, India, the United States, Canada, Antarctica and the Czech Republic.

Since its discovery more than a century ago, very little gem-quality grandidierite has surfaced and most of what has been found is translucent.

However, a 2014 discovery of more transparent material outside of Tarnomaro, Madagascar, near the site where the first pieces of grandidierite were found, has resulted in several fine quality faceted stones, according to the Gemmological Association of Great Britain’s Gems & Jewellery spring issue.

4. It is extremely rare.

Despite the number of sources, grandidierite is still extremely rare; pockets tend to be small and quickly become depleted.

Much of the material that comes out of the ground is opaque, IGS said. As mentioned before, even when gem-quality material is produced, it’s often translucent (semi-transparent), and is thereby cut into cabochons ranging in size from about 1 carat to 10 carats and up.

According to GIA’s Gems & Gemology, gem-quality grandidierite of “facetable size” was “almost unheard of” in the market before the summer of 2015.

Bangkok-based gemstone dealer MultiColour Gems said on its website that the ratio of gem-quality crystals to rough is about 1 in 10,000.

The company noted that the Tranomaro deposit, where the 2014 discovery occurred, has produced only about 60 grams (300 carats) of eye-clean crystals.

Given its rarity, fine grandidierite gems can demand significant prices.

For example, gem dealer and Mineral Art manager Brice Gobin is quoted in the Gems & Jewellery article as saying that a buyer paid $50,000 in 2003 for the first known transparent faceted grandidierite, which weighed only 0.29 carats, a fact confirmed by GIA.

Even so, minimal supply goes hand-in-hand with low demand and a lack of knowledge about the stone among many jewelers, according to Gobin.

“Grandidierite is too rare to be able to provide the jewelry market,” he is quoted as saying. “No supply, no demand; it’s as simple as that.”

5. You can see grandidierite gems in New York right now.

For those who haven’t seen grandidierite in person or are looking for the perfect collector gemstone, one Manhattan gallery provides the perfect opportunity.

Gobin sourced a collection of grandidierite gems from the Tranomaro region of Madagascar over an 18-month period, Gems & Jewellery reported. The selection included some 20 gems weighing between 1 and 9-plus carats.

Three of Gobin’s grandidierite gemstones will be on display at the Wilensky Gallery in New York City through at least June, representing the gallery’s foray into faceted gemstones. 

They weigh 2.86, 3.14 and 4.96 carats and are priced at $69,000, $78,000 and $129,500, respectively.

I was lucky enough to get to see those, too, during a recent WJA event at the gallery, and I’m telling you: Run, don’t walk, to see these gems before they’re gone.