NaNa2 [(Mg; Fe2+ )4 Fe3+ ]Si8 O22 (OH)2

Magnesio-arfvedsonite°c 2001 Mineral Data Publishing, ver sion 1.2
Crystal Data: Monoclinic. Point Group: 2=m: Prismatic crystals, to 9 cm; in matted¯brous aggregates. Twinning: [Simple or lamellar twinning k f100g.]
Physical Properties:
Cleavage: [Perfect on f110g, intersecting at »56± and »124± .]Fracture: [Uneven.] Tenacity: [Brittle.] Hardness = [6] D(meas.) = »3.1{3.3D(calc.) = [3.25]
Optical Properties: Translucent to opaque. Color: Dark bluish green, color zoning common;
yellowish, greenish, or bluish in thin section. Luster: Vitreous.
Optical Class: Biaxial ({). Pleochroism: Strong; X = blue-green; Y = green; Z = pale green.
Orientation: Z = b; X ^ c = 20 ± {40 ± . Dispersion: r > v; strong. Absorption: [X > Y > Z.]® = »1.64{1.67 ¯ = »1.65{1.68 ° = »1.655{1.69 2V(meas.) = 0± { »50 ±Cell Data:¯ = 104:18±

Space Group: C2=m: a = 9.799 (ICDD 23-495).
Z=2b = 17.833

c = 5.273

X-ray Powder Pattern: Norra KÄa rr complex, Sweden. (ICDD 23-495).
3.11 (100), 8.38 (80), 3.24 (35), 2.694 (35), 4.45 (30), 3.38 (30), 5.03 (12)Chemistry: (1)
SiO 253.70
TiO2
0.29
ZrO2
0.05
Al 2 O3
1.85
Fe2 O3 15.27
FeO
3.56

(2)
52.71
0.56
3.13
9.50
7.41

MnO
MgO
CaO
Li 2 O
Na2 O
K2 O

(1)
1.05
9.50
0.21
0.24
10.40
1.34

(2)
0.79
11.19
2.22
0.02
8.35
1.97

F
H2 O+
H2 O¡
¡O = F 2Total

(1)
2.11
1.02
0.36
0.88(2)1.50
1.160.01[0.63]

100.07[99.89]2+(1) Lovozero massif, Russia; corresponds to (Na 2:94 K 0:25 Ca 0:03 ) §=3:22 (Mg 2:06 Fe3+
1: 67 Fe0:43 Al 0:14
Mn0: 13 Ti 0: 03 Li 0:14 )§=4:60 (Si7:82 Al 0:18) §=8:00 O22 [(OH)0:99 F0:97 ] §= 1:96 : (2) Oldonyo Dili, Tanzania;
original total given as 99.69%, corresponding to (Na 2:37 K0:37 Ca 0:35 Li 0:01 ) §=3:10 (Mg 2:44 Fe3+
1: 05
Fe2+
0: 91 Al0:22 Mn 0:10 Ti 0:06 ) §=4:78 (Si7:71 Al 0:29 )§=8:00 O22 [(OH)1:13 F0: 70 O0:17 ] §=2:00 :Polymorphism & Series:

Forms a series with arfvedsonite.

Mineral Group: Amphibole (alkali) group: Fe2+ =(Fe2+ + Mg) < 0.5; Fe3+ =(Fe3+ + Alvi ) ¸ 0.5;
(Na + K)A ¸ 0.5; Na B ¸ 1.34.
Occurrence: As exsolution lamellae in cummingtonite from metamorphosed iron formation;in felsic pegmatites; from so dium metasomatism (fenitization) around some carbonatites; asauthigenic or diagenetic overgrowths on detrital igneous \hornblende."
Association:

Aegirine, braunite, winchite, cummingtonite, albite, biotite.

Distribution: From the Norra KÄarr complex, near GrÄa nna, Sweden. In the Gardiner complex,
beyond the head of the Kangerdlugssuaq Fjord, Greenland. From the Khibiny and Lovozero
massifs, Kola Peninsula, Russia. In the Green River Formation, head of Avintagnia Canyon,
Duchesne Co., Utah, USA. In the Wabush Iron Formation, southwestern Labrador, Newfoundland;near Perkins, and at Mont Saint-Hilaire, Quebec, Canada. From Oldonyo Dili, Tanzania. On
Mbolwe Hill, Mkushi River area, Central Province, Zambia. From Ambatoharina, Madagascar. In
the Kajlidongri and Tirodi mines, Madhya Pradesh, India. In the Modatamagawa mine, Noda,
Iwate Prefecture, Japan. Other localities are known.
Name:

For its high magnesium content and similarity to arfvedsonite.

Type Material:n.d.

References: (1) Deer, W.A., R.A. Howie, and J. Zussman (1963) Rock-forming minerals,
v. 2, chain silicates, 364{374. (2) McKie, D. (1966) Fenitization. In: O.F Tuttle and J. Gittins,Eds., Carbonatites. Interscience, New York, 261{294. (3) Phillips, W.R. and D.T. Gri®en (1981)
Optical mineralogy, 243{245.
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