Grandidierite (gran-dih-dee-er-aite) is a rare aquamarine-blue to sea-green gemstone. It’s mostly known among collectors, more than everyday gem buyers. But one look at grandidierite will show you that it’s not a gem to pass over!

Just how rare is grandidierite? Extremely rare. To put it in perspective, the Gemological Institute of America (GIA) reported that, before summer 2015, gem-quality grandidierite crystals big enough to be faceted were “almost unheard of.”

Among the rarest gemstones in the world, grandidierite often makes top ten and even sometimes top five lists.

So, is grandidierite a good investment? What makes it unique? By the end of this guide, you’ll know all the answers you need to determine if grandidierite is a gem for you!

What Is The Gemstone Grandidierite?

First, is grandidierite a precious stone? No, grandidierite is a semi-precious gemstone, though it’s rarer and usually more expensive than the four precious gemstones (diamond, emerald, ruby, and sapphire).

Though it’s not a more affordable alternative, grandidierite can substitute zircon as a traditional December birthstone or aquamarine as a March birthstone. Grandidierite cabochons can also resemble jade, making them substitutable as an August birthstone as well.

The gem’s blue and green tones mean that grandidierite can be used as a zodiac stone for earth signs (Taurus, Virgo, and Capricorn) and air signs (Gemini, Libra, and Aquarius).

Mineral-wise, what kind of stone is grandidierite?

Grandidierite Specifications & Characteristics

Grandidierite is a magnesium aluminum borosilicate stone. The exact formula varies by source, sometimes written as (Mg,Fe)Al3BSiO9, other times as (Mg,Fe)Al3(BO4)(SiO4)O, and still other times as (Mg,Fe2+)(Al,Fe3+)3(SiO4)(BO3)O2.

The (Mg,Fe) part of its composition accounts for the frequent presence of iron and manganese impurities. Other impurities include titanium, sodium, and potassium, but iron causes the characteristic blue-green hue.

Speaking of which, grandidierite’s color is the first key to its identification. The stone only occurs in shades of blue, green, or blue-green. The stone’s pleochroism(ability to display different colors from different viewing angles) is also a distinguishing feature.

However, lazulite has similar coloring andsimilar pleochroic colors. Grandidierite has a slightly higher Mohs hardness(lazulite is 5.5-6), but lazulite has a higher refractive index (1.60-1.66) and density (3.08-3.83).

Here are the remaining grandidierite mineral properties:

• Mohs hardness: 7.5

• Color: Blue, green, blue-green, green-blue

• Crystal structure: Orthorhombic

• Luster: Vitreous (glassy), pearly on cleavage

• Transparency: Transparent to opaque

• Refractive index: 1.58-1.63

• Density: 2.85-3.00

• Cleavage: Perfect on [100]; Good/Distinct on [010]

• Fracture: Uneven

• Streak: White

• Luminescence: None

• Pleochroism: Present and strong in dark green, colorless/pale yellow, and dark blue-green

Now that you know the mineralogy, it’s time to get into the symbolism and history of grandidierite!