igneous
Arfvedsonite with Garnet
Na3(Fe2+,Mg)4Fe3+Si8O22(OH)2
Hardness: 5.5-6 (Mohs); Color: Black to dark bluish-gray with pink/red garnet inclusions; Luster: Vitreous to silky; Crystal Structure: Monoclinic; Cleavage: Perfect amphibole cleavage at 56 and 124 degrees; Specific Gravity: 3.44
- Hardness
- 5
- Color
- Black to dark bluish-gray with pink/red garnet inclusions
- Luster
- Vitreous to silky
Identified More igneous →
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Physical properties
Hardness: 5.5-6 (Mohs); Color: Black to dark bluish-gray with pink/red garnet inclusions; Luster: Vitreous to silky; Crystal Structure: Monoclinic; Cleavage: Perfect amphibole cleavage at 56 and 124 degrees; Specific Gravity: 3.44
Formation & geological history
Forms in alkaline igneous rocks like nepheline syenites and granitic pegmatites through crystallization from silica-poor, alkali-rich magmas, often during late-stage magmatic processes.
Uses & applications
Primarily used as a decorative material, in lapidary arts (towers, spheres, beads), and for mineral collecting.
Geological facts
Arfvedsonite is often confused with Astrophyllite or Nuummite due to its dark color and occasional flash, but its distinct crystal structure and association with red garnet spots help identify it.
Field identification & locations
Collectors should look for the characteristic dark black/blue needle-like crystals and 'fire' flashes. Major deposits are found in Greenland (Ilimaussaq complex), Canada (Mont Saint-Hilaire), and Russia (Kola Peninsula).
