The facts
What grandidierite actually is
Mineralogically, grandidierite is grandidierite — (Mg,Fe)Al₃(BO₃)(SiO₄)O₂, crystallising in the orthorhombic system.
The colour is caused by iron. That is worth knowing because it determines what heating, light and time can and cannot do to the stone.
A refractometer reads 1.583–1.639, and the specific gravity sits near 2.98–3.00; cleavage is perfect, one direction.
Where grandidierite comes from
The recognised sources are Tranomaro and Andrahomana, Madagascar and Sri Lanka.
Origin affects price in this material, so we name the locality on every quote rather than the country. "African" or "Asian" tells a buyer nothing.
Is grandidierite treated?
None.
That makes disclosure simple: there is nothing to declare. It also means a seller offering a "treated" version of this material is offering something else.
What grandidierite is confused with
The usual confusions are Grandidierite–ominelite series, Apatite and Aquamarine.
The separation is rarely a matter of opinion: refractive index 1.583–1.639 and specific gravity 2.98–3.00 settle most of it in a minute, and magnification settles the rest.
What grandidierite is used for
Grandidierite is bought by mineral collecting and jewellery — and each of those trades wants a different form of the same material.
We quote each application in the unit that trade actually buys in, by the specimen or by the carat.
Durability and care
Hardness 7–7.5; cleavage perfect, one direction. That combination decides what it can safely be set into.
Hardness is not the whole story. Perfect cleavage means the stone can split cleanly if struck along the wrong plane, whatever its Mohs number, so a protective setting matters more here than the hardness suggests.
Warm water, mild soap and a soft brush. Avoid ultrasonic cleaners on anything fracture-filled, stabilised, dyed or visibly included.
What grandidierite costs
Indicative pricing for grandidierite is $2,000–20,000/ct.
That is a range, not a quote. Colour, size, clarity, cut and origin move the figure a long way inside it, and the only honest price is one given against a specific stone. Send us what you need and we will price it.
Questions
Is grandidierite treated?
None.
Where does grandidierite come from?
Tranomaro and Andrahomana, Madagascar and Sri Lanka. Origin affects price, so we name the locality rather than the country on every quote.
Is grandidierite hard enough to wear every day?
With care. It is 7–7.5 on the Mohs scale, which is hard enough, but perfect, one direction cleavage means it can split if struck at the wrong angle. Use a protective setting and avoid ultrasonic cleaning.
How much does grandidierite cost?
Indicatively $2,000–20,000/ct. Colour, size, clarity and origin move the price a long way within that, so treat it as a range and ask for a quote against a specific stone.
What is grandidierite confused with?
Most often Grandidierite–ominelite series, Apatite and Aquamarine. A refractive index of 1.583–1.639 and a specific gravity near 2.98–3.00 separate it quickly.
Related stones
Looking for grandidierite?
Tell us the size, the quality and what it is for. We source it, photograph it and quote it — with the locality named.
Ask about grandidierite