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The arfvedsonite Mineral Group
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Arfvedsonite was first discovered in 1823. It is named after Johan August Arfwedson (1792–1841), a Swedish chemist credited with the discovery of the element lithium. Arfvedsonite is not a common mineral, and is found only in a limited amount of localities throughout the world. However, several of these deposits have produced outstanding examples of this mineral, making it a very collectible species. There are
several variations of Arfvedsonite with different elemental
substitutions. Some of these are recognized as individual minerals,
thereby making Arfvedsonite a mineral group, with Arfvedsonite the
dominating member. |
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Chemical Formula |
NaNa2Fe2+4Fe3+Si8O22(OH)2 |
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Composition |
Basic sodium iron silicate, sometimes with some potassium, magnesium, and fluorine
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| Variable Formula |
(Na,K)Na2(Fe2+,Mg)4Fe3+Si8O22(OH,F)2
The above formula encompasses all the recognized member minerals of the extended Arfvedsonite group
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Color |
Greenish-black, grayish black, reddish-brown, dark brown, black |
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Streak |
Dark bluish-gray |
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Hardness |
5.5 - 6 |
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Crystal System |
Monoclinic |
Crystal Forms
and Aggregates |
In elongated prismatic crystals, often frozen in a matrix or spraying out of the matrix. Also in stubby crystals, wedge-shaped crystals, and in interconnected groups of crystals. Frequently acicular, radiating, reticulated, and columnar. Crystals are typically striated lengthwise.
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Transparency |
Opaque. May be translucent on thin cross-sections under back-lighting. |
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Specific Gravity |
3.1 - 3.5 |
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Luster |
Vitreous |
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Cleavage |
1,2 - prismatic |
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Fracture |
Splintery, uneven |
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Tenacity |
Brittle |
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In Group |
Silicates; Inosilicates; Amphibole Group |
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Striking Features |
Crystal habits and mode of occurrence. |
| Environment |
In iron-rich alkaline rocks in nepheline syenite deposits.
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| Rock Type |
Igneous, Metamorphic |
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Popularity (1-4)
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2 |
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Prevalence (1-3)
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3 |
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Demand (1-3) |
2 |
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- Variety of Arfvedsonite where magnesium partially replaces one the
iron, and where fluorine partially replaces the hydroxyl and dominates it. Fluro-magnesio-arfvedsonite is
recognized by the IMA as a distinct mineral
species with the following chemical
formula: NaNa2(Mg,Fe2+)4Fe3+Si8O22(F,OH)2
- Manganese-rich variety of Arfvedsonite with a reddish brown to bronze color, found mostly in Tirodi, India. Juddite is named after John Wesley Judd (1840 – 1916), a geologist for the British Geological Survey and later a professor of geology at the Imperial College in London.
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Arfvedsonite is used as a collector's mineral. The highly aesthetic mineral specimens from Malawi are especially popular.
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Some of the best examples of Arfvedsonite, in the form of highly lustrous,
slender black crystals, are well known at Mount Malosa, Zomba District,
Malawi. They may be individual prismatic crystals, which can exceptionally
large, or they can be on an aesthetically contrasting matrix of white
feldspar. They also may form a needle-like pseudomorph after Aegirine in that locality.
A manganese-rich form of Arfvedsonite with a reddish color, sometimes known as Juddite, comes from Tirodi, Madhya Pradesh, India. Well-terminated, lustrous Arfvedsonite crystals have recently been coming from Imilchil, Er Rachidia Province, Morocco. In Greenland, elongated crystals associated with feldspar were found in the Ilimaussaq complex, Narsuq.
Arfvedsonite is uncommon in the U.S. The best crystals come from Hurricane Mountain, North Conway, Carroll Co., New Hampshire; and Washington Pass, Okanogan Co., Washington. In Canada, large, thick, and lustrous Arfvedsonite crystals have come from Mont Saint Hilaire, Quebec.
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Aegirine - Crystals have steep pyramidal terminations.
Schorl - Harder and lacks good cleavage.
Riebeckite - Can be very difficult to distinguish, although usually in thicker crystals.
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