Grandidierite Gem Guide and Properties Chart

Grandidierite is a greenish blue or bluish green mineral named after French explorer and naturalist Alfred Grandidier. The mineral was originally discovered on the southern coast of Madagascar in the Andrahomana area. A new gem quality deposit was found near Tranomaro, Madagascar in 2014.

General Information

Classification
Optical Properties
Characteristic Physical Properties
Chemistry & Crystallography

Common Name

Grandidierite

Species

Grandidierite

Transparency

Transparent-Translucent

Dispersion

Strength: Strong Fire

Refractive Index

1.590-1.639

Birefringence

0.033- 0.037

Optic Character

Biaxial

Optic Sign

Negative

Polariscope Reaction

Aggregate (AGG), Doubly Refractive (DR)

Fluorescence

SWUV: Inert
LWUV: Inert

Pleochroism

Trichroic, pale yellow to colorless, greenish blue, and blue or greenish blue, blue-green and colorless

Hardness

7-7.5

Streak

White

Specific Gravity

2.85-3.010

Toughness

Good

Inclusions

Apatite, monazite, and zircon crystals, liquid and 2-phase inclusions. Parallel growth planes.

Luster

Vitreous

Fracture

Uneven

Cleavage

Good, Distinct

Chemical Name

magnesium aluminum borosilicate

Chemical Formula

(Mg,Fe)Al₃(BO₄)(SiO₄)O

Crystal System

Orthorhombic

Chemistry Classification

Silicate

Grandidierite Colors

Green
Green
Blue
Green

Countries of Origin

Unknown; Madagascar

Care

Normal care