| Mineral | RIEBECKITE |
| Chemistry | []Na 2 [Fe 2+ 3 Fe 3+ 2 ][Si 8 O 22 ](OH) 2 |
| Color | Light blue to blue -black . |
| Luster | Vitreous |
| CrystalSystem | Monoclinic |
| CrystalHabits | include slender prismatic to acicular, oftenaggregated crystals, columnar, granular and fibrous, asbestiform masses.A moss-like aggregate habit has been described when found in some igneousrocks. |
| Hardness | 5 - 5½ |
| Streak | Pale grey to bluish-grey. |
| Characteristics | Weakly pleochroic and crystals are striatedlengthwise. |
| Occurences | include Socotra Island, South Yemen; Transvaal,South Africa; Schirmeck, Germany; Langesund, Norway; Krivoi Rog, Ukraine;Hamersley Range in Western Australia; Scotland; Madagascar; Quincy, Massachusetts;St Peter s Dome, El Paso County, Colorado; California; Oregon and CumberlandHill, Rhode Island, USA. |
| Indicators | crystal habit, color, streak, cleavageand hardness. |
| DensityNote | average to slightlyabove average |
| IMAStatus | Approved |
| CellParameters | a = 9.76b = 18.04c = 5.33 β=103.59° |
| Ratio | a:b:c = 0.541 : 1 : 0.295 |
| OpticalType | Biaxial (-) |
| RI | n α =1.680 - 1.698 n β =1.683 - 1.700 n |
| Birefringence | δ=0.005 - 0.008 |
| SurfaceRelief | High |
| Strunz | 8/F.08-50 8 : Silicates F : Inosilicates (chain and band) double chains [Si2O6]4- 08 : Amphibole groupGlaucophane - Riebeckite - Kozulite series |
