Riebeckite
| Colour | Blue, Black |
|---|---|
| Mohs hardness | 6 |
| Lustre | Vitreous to silky |
| Streak | Pale to bluish gray |
| Crystal system | Monoclinic |
| Transparency | Semitransparent |
| Cleavage | Perfect on {110}, intersecting at 56° and 124°; partings on {100} and {010} |
| Fracture | Conchoidal to uneven |
| Chemical formula | Na 2 (Fe 2+ 3 Fe 3+ 2 )Si 8 O 22 (OH) 2 |
| Specific gravity | 3.28–3.44 |
What is Riebeckite?
Riebeckite is a sodium-rich member of the amphibole group of silicate minerals, chemical formula Na2(Fe2+3Fe3+2)Si8O22(OH)2. It forms a solid solution series with magnesioriebeckite. It crystallizes in the monoclinic system, usually as long prismatic crystals showing a diamond-shaped cross section, but also in fibrous, bladed, acicular, columnar, and radiating forms. Its Mohs hardness is 5.0–6.0, and its specific gravity is 3.0–3.4. Cleavage is perfect, two directions in the shape of a rhombus; fracture is uneven, splintery. It is often translucent to nearly opaque.
How to identify Riebeckite
- Lustre: Vitreous to silky.
- Hardness: Mohs 6 — about as hard as a steel knife.
- Streak: Pale to bluish gray.
- Habit: Monoclinic crystal system.
Riebeckite in different forms
Stones often confused with Riebeckite
Frequently asked questions
How hard is Riebeckite?
Riebeckite is Mohs 6 on the hardness scale.
What colour is Riebeckite?
Riebeckite is typically blue, black (Black, dark blue; dark blue to yellow-green in thin section).