Arfvedsonite

Arfvedsonite is a sodium amphibole mineral with composition: Na3(Fe,Mg)4FeSi8O22(OH)2: sodium, iron, magnesium, inosilicate, hydroxide. It crystallizes in the monoclinic prismatic crystal system and typically occurs as greenish black to bluish grey fibrous to radiating or stellate prisms. It has a specific gravity of 3.44 to 3.45 and a Mohs hardness of 5.5 to 6. Refractive indices are nα=1.652 - 1.699, nβ=1.660 - 1.705, and nγ=1.666 - 1.708.
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General Information:
 Chemical Formula:
NaNa2(Fe++4Fe+++)Si8O22(OH)2
 Composition:
(Molecular Weight = 958.89 gm)
Sodium 7.19 % Na
Iron 29.12 % Fe
Silicon 23.43 % Si
Hydrogen 0.21 % H 
Oxygen 40.04 % O 
 Empirical Formula:
Na3Fe-2+4Fe-3+(Si8O22)(OH)2
 Environment:
Igneous syenites and pegmatites.
 IMA Status:
Approved IMA 1978
 Locality:
Boulder Co., Colorado.
 Name Origin:
Named after the Swedish chemist, J. A. Arfvedson (1792-1841).
Physical Properties:
 Cleavage:
[110] Perfect, [???] Imperfect
 Color:
black, grayish green, or bluish gray.
 Density:
3.44 - 3.45, Average = 3.44
 Diaphaniety:
Translucent to opaque
 Habits:
Radial - Crystals radiate from a center without producing stellar forms (e.g. stibnite), Fibrous - Crystals made up of fibers., Stellate - Occurs as spherical, radial aggregates radia ting from a "star" like point.
 Hardness:
5.5-6 - Knife Blade-Orthoclase
 Luminescence:
Non-fluorescent.
 Luster:
Vitreous (Glassy)
 Streak:
bluish gray
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General Information:
 Chemical Formula:
NaNa2(Mg4Fe++)Si8O22(OH)2
 Composition:
(Molecular Weight = 832.72 gm)
Sodium 8.28 % Na
Magnesium 11.67 % Mg
Iron 6.71 % Fe
Silicon 26.98 % Si
Hydrogen 0.24 % H 
Oxygen 46.11 % O 
 Empirical Formula:
Na3Mg4Fe3+(Si8O22)(OH)2
 IMA Status:
Approved IMA 1978
Physical Properties:
 Color:
black or gray.
 Density:
3.17
 Diaphaniety:
Subopaque
 Hardness:
5-6 - Between Apatite and Orthoclase
 Luster:
Vitreous (Glassy)
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ARFVEDSONITE

B: (Kimia) arfedsonit
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