Fenaksite Mineral Data

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General Fenaksite Information

Chemical Formula:

(K,Na,Ca)4(Fe++,Fe+++,Mn)2Si8O20(OH,F)

Composition:

Molecular Weight = 806.42 gm

Potassium 8.73 % K 10.51 % K₂O

Sodium 4.28 % Na 5.76 % Na₂O

Calcium 3.48 % Ca 4.87 % CaO

Manganese 2.04 % Mn 2.64 % MnO

Iron 11.77 % Fe 11.58 % FeO / 3.96 % Fe₂O₃

Silicon 27.86 % Si 59.61 % SiO₂

Hydrogen 0.10 % H 0.89 % H₂O

Oxygen 41.27 % O

Fluorine 0.47 % F 0.47 % F

- % F -0.20 % -O=F₂

______ ______

100.00 % 100.10 % = TOTAL OXIDE

Empirical Formula:

K_1.8Na_1.5Ca_0.7Fe²⁺_1.3Fe³⁺_0.4Mn²⁺_0.3Si₈O₂₀(OH)_0.8F_0.2

Environment:

In pegmatites associated with an ijolite-urtite intrusion in a differentiated alkalic massif.

IMA Status:

Approved IMA 1959

Locality:

On Mts. Rasvumchorr and Yukspor, Khibiny massif, Kola Peninsula, Russia. Link to MinDat.org Location Data.

Name Origin:

Named for the Fe, Na, K, and Si in the formula.

Name Pronunciation:

Fenaksite + Pronunciation

Synonym:

ICSD 20098

PDF 13-520

Fenaksite Image

Images:

Fenaksite

Comments: Tan to rose colored crystalline fenaksite with dark green-black crystalline pyroxene.
Location: Khibiny Massif, Kola Peninsula, Murmansk District, Russia. Scale: See Photo.
© Jeff Weissman / Photographic Guide to Mineral Species

Fenaksite Crystallography

Axial Ratios:

a:b:c =0.847:1:1.2111

Cell Dimensions:

a = 6.98, b = 8.24, c = 9.98, Z = 1; alpha = 114.2°, beta = 80.22°, gamma = 115.6° V = 465.30 Den(Calc)= 2.88

Crystal System:

Triclinic - PinacoidalH-M Symbol ( 1) Space Group: P1

$Help on X Ray Diffraction:$ X Ray Diffraction:

By Intensity(I/I_o): 3.03(1), 2.46(0.7), 3.55(0.7),

Crystal Structure:

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Rozhdestvenskaya I V , Bannova I I , Nikishova L V , Soboleva T V , Doklady Earth Sciences , 398 (2004) p.1029-1033, The crystal structure of fenaksite K2Na2Fe2Si8O20, Locality: synthetic

Physical Properties of Fenaksite

Cleavage:

{100} Good, {010} Good

Color:

Brown, Light pink.

Density:

2.744

Diaphaneity:

Transparent to Translucent

Habit:

Granular - Generally occurs as anhedral to subhedral crystals in matrix.

Hardness:

5-5.5 - Apatite-Knife Blade

Luster:

Pearly

Streak:

white

Optical Properties of Fenaksite

Gladstone-Dale:

CI meas= 0.028 (Excellent) - where the CI = (1-KPDmeas/KC)
CI calc= 0.061 (Fair) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.1958,KPDmeas= 0.2026,KC= 0.2085
Ncalc = 1.57 - 1.59

Optical Data:

Biaxial (+), a=1.541, b=1.56, g=1.567, bire=0.0260, 2V(Calc)=60, 2V(Meas)=84.

Calculated Properties of Fenaksite

Electron Density:

Bulk Density (Electron Density)=2.70 gm/cc
note: Specific Gravity of Fenaksite =2.74 gm/cc.

Fermion Index:

Fermion Index = 0.01
Boson Index = 0.99

Photoelectric:

PE_Fenaksite= 6.44 barns/electron
U=PE_Fenaksite x r_electron= 17.41 barns/cc.

Radioactivity:

GRapi = 124.09 (Gamma Ray American Petroleum Institute Units)
Concentration of Fenaksite per GRapi unit = 0.81 (%)

Estimated Radioactivity from Fenaksite - barely detectable

Fenaksite Classification

Dana Class:

70.01.01.02 (70)Inosilicate Column or Tube Structures

(70.01)with columnar silicate units

(70.01.01)Litidionite group

70.01.01.01 Litidionite KNaCuSi4O10 P1 1

70.01.01.02 Fenaksite (K,Na,Ca)4(Fe,Fe,Mn)2Si8O20(OH,F) P1 1

70.01.01.03 Manaksite KNaMnSi4O10 P1 1

70.01.01.04 Agrellite NaCa2Si4O10F P1 1

Strunz Class:

09.DG.70 09 - SILICATES (Germanates)

09.D - Inosilicates* Structural terminology according to Liebau (1985)

09.DG -Inosilicates with 3-periodic single and multiple chains

09.DG.70 Fenaksite (K,Na,Ca)4(Fe,Fe,Mn)2Si8O20(OH,F) P1 1

09.DG.70 Manaksite KNaMnSi4O10 P1 1

Other Fenaksite Information

References:

NAME( AntBidBlaNic2) PHYS. PROP.(AntBidBlaNic2) OPTIC PROP.(Enc. of Minerals,2nd ed.,1990)

See Also:

Links to other databases for Fenaksite :
1 - Am. Min. Crystal Structure Database
2 - Athena
3 - EUROmin Project
4 - Ecole des Mines de Paris
5 - GeoScienceWorld
6 - Google Images
7 - Google Scholar
8 - Handbook of Mineralogy (MinSocAm)
9 - Handbook of Mineralogy (UofA)
10 - MinDAT
11 - Mineralienatlas (Deutsch)
12 - Online Mineral Museum
13 - QUT Mineral Atlas
14 - Ruff.Info
15 - WWW-MINCRYST

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Fenaksite

(K,Na,Ca)4(Fe++,Fe+++,Mn)2Si8O20(OH,F)
Dana No: 70.01.01.02 Strunz No: 09.DG.70
Locality:

Notes: