Fayalite Mineral Data

Fayalite Mineral Data +

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General Fayalite Information

Chemical Formula:

Fe++2SiO4

Composition:

Molecular Weight = 203.78 gm

Iron 54.81 % Fe 70.51 % FeO

Silicon 13.78 % Si 29.49 % SiO₂

Oxygen 31.41 % O

______ ______

100.00 % 100.00 % = TOTAL OXIDE

Empirical Formula:

Fe²⁺₂(SiO₄)

Environment:

Ultra mafic silica-poor igneous rocks.

IMA Status:

Valid Species (Pre-IMA) 1840

Locality:

Fayal Island, Azores Link to MinDat.org Location Data.

Name Origin:

Named for the locality

Synonym:

Hortonolite - Mn,Mg

ICSD 26375

Knebelite(Mn)

PDF 31-633

Fayalite Image

Images:

Fayalite

Comments: Flattened crystals of fayalite on cristobalite.
Location: Coso Hot Springs, Inyo County, California. Scale: Not Given.
© Lou Perloff / Photo Atlas of Minerals

Fayalite Crystallography

Axial Ratios:

a:b:c =0.4666:1:0.5862

Cell Dimensions:

a = 4.76, b = 10.2, c = 5.98, Z = 4; V = 290.34 Den(Calc)= 4.66

Crystal System:

Orthorhombic - DipyramidalH-M Symbol (2/m 2/m 2/m) Space Group: Pbnm

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

By Intensity(I/I_o): 2.831(1), 2.501(0.7), 2.566(0.5),

Crystal Structure:

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Birle J D , Gibbs G V , Moore P B , Smith J V , American Mineralogist , 53 (1968) p.807-824, Crystal structures of natural olivines

View Additional jPOWD Structure files for Fayalite
[1] [10] [11] [2] [3] [4] [5] [6] [7] [8] [9]

Physical Properties of Fayalite

Cleavage:

[010] Indistinct

Color:

Brown, Black, Black.

Density:

4.39

Diaphaniety:

Transparent to Translucent

Fracture:

Conchoidal - Fractures developed in brittle materials characterized by smoothly curving surfaces, (e.g. quartz).

Habit:

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

Habit:

Massive - Granular - Common texture observed in granite and other igneous rock.

Hardness:

6.5 - Pyrite

Luminescence:

None.

Luster:

Vitreous (Glassy)

Streak:

white

Optical Properties of Fayalite

Gladstone-Dale:

CI meas= 0.055 (Good) - where the CI = (1-KPDmeas/KC)
CI calc= 0.11 (Poor) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.1726,KPDmeas= 0.1833,KC= 0.1939

Optical Data:

Biaxial (-), a=1.731-1.824, b=1.76-1.864, g=1.773-1.875, bire=0.0420-0.0510, 2V(Calc)=54-66, 2V(Meas)=74-47. Dispersion weak, r > v.

Pleochroism (x):

greenish yellow, pale yellow, or pale amber.

Pleochroism (y):

orange yellow, orange yellow, or orange yellow.

Pleochroism (z):

greenish yellow, pale yellow, or pale amber.

Calculated Properties of Fayalite

Electron Density:

r_electron=4.22 gm/cc
note: r_Fayalite=4.39 gm/cc.

Fermion Index

Fermion Index = 0.0182
Boson Index = 0.9818

Photoelectric:

PE_Fayalite= 17.09 barns/electron
U=PE_Fayalite x r_electron= 72.16 barns/cc.

Radioactivity:

GRapi = 0 (Gamma Ray American Petroleum Institute Units)

Fayalite is Not Radioactive

Fayalite Classification

Dana Class:

51.3.1.1 (51)Nesosilicate Insular SiO4 Groups Only

(51.3)with all cations in octahedral [6] coordination

(51.3.1)Olivine group

51.3.1.0 Olivine* (Mg,Fe)2SiO4 Pbnm 2/m 2/m 2/m

51.3.1.1 Fayalite Fe2SiO4 Pbnm 2/m 2/m 2/m

51.3.1.2 Forsterite Mg2SiO4 Pbnm 2/m 2/m 2/m

51.3.1.3 Liebenbergite (Ni,Mg)2SiO4 Pbnm 2/m 2/m 2/m

51.3.1.4 Tephroite Mn2SiO4 P nma 2/m 2/m 2/m

51.3.1.5 Laihunite FeFe2(SiO4)2 P 2₁/b 2/m

Strunz Class:

VIII/A.04-20 VIII - Silicates

VIII/A - Nesosilicates with [SiO4]4-groups, cations of octahedral orientation [6]

VIII/A.04 - Olivine group

VIII/A.04-10 Forsterite Mg2SiO4 Pbnm 2/m 2/m 2/m

VIII/A.04-20 Fayalite Fe2SiO4 Pbnm 2/m 2/m 2/m

VIII/A.04-30 Tephroite Mn2SiO4 P nma 2/m 2/m 2/m

VIII/A.04-40 Liebenbergite (Ni,Mg)2SiO4 Pbnm 2/m 2/m 2/m

VIII/A.04-50 Laihunite FeFe2(SiO4)2 P 2₁/b 2/m

Other Fayalite Information

References:

NAME( Ford32) PHYS. PROP.(Enc. of Minerals,2nd ed.,1990) OPTIC PROP.(Heinrich65)

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Print or Cut-and-Paste your Fayalite Specimen Label here :

Fayalite

Fe++2SiO4
Dana No: 51.3.1.1 Strunz No: VIII/A.04-20
Locality:

Notes: