Arfvedsonite
NaNa2(Fe2+4Fe3+)Si8O22(OH)2 [CNMNC approved formula]
Named after the Swedish chemist, J. A. Arfvedson (1792-1841). Named as Arfwedsonite in 1823.
| IMA status : | Approved Species 1997 () |
| CLASSIFICATION | |
| Dana (8th edition) : |
66.01.03c.09 |
| (66) Inosilicate Double-Width Unbranched Chains, W=2 | |
| (66.01) with P=2 amphibole configuration | |
| (66.01.03c) Group 4, the sodic amphiboles | |
| Nickel-Strunz (10th edition) : |
09.DE.25 |
| (09) Silicates | |
| (09.D) Inosilicates* Structural terminology per Liebau (1985) | |
| (09.DE) with 2-periodic double chains, Si4O11; Clinoamphiboles | |
| Crystal system: | Monoclinic System |
| Point group (H-M): | 2/m — prismatic |
| Unit cell: | a = 10.007Å, b = 18.077Å, c = 5.332Å β = 104.1° |
| Crystal Habit: | Crystals short to long prismatic, often tabular; prismatic aggregates and radiating fibrous clusters |
| Color: | Greenish black |
| Diaphaneity: | Translucent to nearly opaque |
| Luster: | Vitreous |
| Hardness (Mohs): | 5 - 6 |
| Measured Density: | 3.37 - 3.50 g/cm3 |
| Cleavage: | 2; {110} perfect, {010} parting |
| Tenacity: | Brittle |
| Fracture: | Uneven |
| Streak: | Dark bluish grey-green |
| Polymorphism and Series: | Forms a series with magnesio-arfvedsonite. |
| Geologic Setting: | Common in alkalic granites and other alkalic plutonic rocks and pegmatites. |
| Mineral Association: | Nepheline, albite, aegirine, riebeckite, katophorite, magnesio-katophorite, quartz |
Arfvedsonite with aegirine on orthoclaseOrigin: Mt. Maloso, Malawi
Sample size: 6.5 x 5 x 4 cm
Photo: Rob Lavinsky
(zoom-in of above)
2-4 cm long arvedsonite crystals with 2-6 mm eudialyteand yellow-brown rinkite
Origin: Kangersluarssak, Ilimaussaq Intrusion, Greenland, Denmark
Sample size: 5 x 6 cm
Photo: Diederik Visser