Grandidierite
Mineral (Mg,Fe)Al3(BO3)(SiO4)O2
About it
A rare bluish-green gem species, strongly pleochroic, named for French explorer Alfred Grandidier; translucent gem rough comes from southern Madagascar.
- Type
- Mineral
- Group
- Silicate (nesosilicate), grandidierite group
- Formula
- (Mg,Fe)Al3(BO3)(SiO4)O2
- Hardness (Mohs)
- 7.5
- Specific gravity
- 2.85–3
- Streak
- white
- Lustre
- vitreous (glassy), pearly
- Crystal system
- Orthorhombic
- Colours
- bluish green, greenish blue
- Transparency
- transparent, translucent
- Cleavage and fracture
- perfect in one direction
Typical values: real specimens vary. For more, see mindat.org.