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Fayalite

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Big Photo

Caspar quarry, Bellerberg volcano, Ettringen, Mayen, Eifel, Rhineland-Palatinate, Germany
© Stephan Wolfsried

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Formula:
Fe
2+
2
SiO
 
4
System:OrthorhombicColour:Greenish-yellow, yellow ...
Lustre:Vitreous, GreasyHardness:7
Member of:Olivine Group
Name:Named by Gmelin in 1840 for the type locality, Faial Island (Fayal Island), Azores District (Azores Islands), Portugal.


Olivine Group. Fayalite-Forsterite Series, and the Fayalite-Tephroite Series. The Fe2+ analogue of Forsterite, Tephroite, and Calcio-Olivine.

Very rare in nature, but common in man-made (metallurgy) iron slags.
See also laihunite.

Visit gemdat.org for gemological information about Fayalite. Currently in public beta-test.

Classification of Fayalite

IMA status:Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
Strunz 8th edition ID:8/A.04-20
Nickel-Strunz 10th (pending) edition ID:9.AC.05

9 : SILICATES (Germanates)
A : Nesosilicates
C : Nesosilicates without additional anions; cations in octahedral [6] coordination
Dana 8th edition ID:51.3.1.1

51 : NESOSILICATES Insular SiO4 Groups Only
3 : Insular SiO4 Groups Only with all cations in octahedral [6] coordination
Hey's CIM Ref.:14.19.1

14 : Silicates not Containing Aluminum
19 : Silicates of Fe
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Type Occurrence of Fayalite

Type Locality:Faial Island (Fayal Island), Azores District, Portugal
Year of Discovery:1840

Physical Properties of Fayalite

Lustre:Vitreous, Greasy
Diaphaneity (Transparency):Transparent, Translucent
Colour:Greenish-yellow, yellow or brown
Streak:Colourless
Hardness (Mohs):7

Crystallography of Fayalite

Crystal System:Orthorhombic
Cell Parameters:a = 4.79Å, b = 10.39Å, c = 6.06Å
Ratio:a:b:c = 0.461 : 1 : 0.583
Unit Cell Volume:V 301.59 ų (Calculated from Unit Cell)

Optical Data of Fayalite

Type:Biaxial (-)
RI values: nα = 1.731 - 1.824 nβ = 1.760 - 1.864 nγ = 1.773 - 1.875
2V:Measured: 74° to 47°, Calculated: 54° to 66°
Maximum Birefringence:δ = 0.042 - 0.051

Chart shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:Very High
Dispersion:weak

Chemical Properties of Fayalite

Formula:
Fe
2+
2
SiO
 
4
Essential elements:Fe, O, Si
All elements listed in formula:Fe, O, Si
Common Impurities:Mn

Relationship of Fayalite to other Species

Series:Forms a series with Forsterite (see here)
Forms a series with Forsterite (see here)
Forms a series with Tephroite (see here)
Member of:Olivine Group
Other Members of Group:

- +
Calcio-Olivine
Ca
 
2
SiO
 
4
Forsterite
Mg
 
2
SiO
 
4
Glaucochroite
CaMn
2+
 
SiO
 
4
Kirschsteinite
CaFe
2+
 
SiO
 
4
Laihunite
Fe
2+
 
Fe
3+
2
(SiO
 
4
)
 
2
Liebenbergite
(Ni,Mg)
 
2
SiO
 
4
Monticellite
CaMgSiO
 
4
Olivine
(Mg,Fe
2+
 
)
 
2
SiO
 
4
Tephroite
Mn
2+
2
SiO
 
4
Related Minerals - Nickel-Strunz Grouping):

- +
9.AC.05Forsterite
Mg
 
2
SiO
 
4
9.AC.05Glaucochroite
CaMn
2+
 
SiO
 
4
9.AC.05Kirschsteinite
CaFe
2+
 
SiO
 
4
9.AC.05Laihunite
Fe
2+
 
Fe
3+
2
(SiO
 
4
)
 
2
9.AC.05Liebenbergite
(Ni,Mg)
 
2
SiO
 
4
9.AC.05Tephroite
Mn
2+
2
SiO
 
4
9.AC.10Monticellite
CaMgSiO
 
4
9.AC.15Brunogeierite
Fe
2+
2
Ge
4+
 
O
 
4
9.AC.15Ringwoodite
(Mg,Fe
2+
 
)
 
2
SiO
 
4
9.AC.20Chesnokovite
Na
 
2
[SiO
 
2
(OH)
 
2
] · 8H
 
2
O
Related Minerals - Hey's Index Grouping:

- +
14.19.2Ferrosilite
FeSiO
 
3
14.19.3Laihunite
Fe
2+
 
Fe
3+
2
(SiO
 
4
)
 
2
14.19.4Ferro-anthophyllite
☐{Fe
2+
2
}{Fe
2+
5
}(Si
 
8
O
 
22
)(OH)
 
2
14.19.5Ferripyrophyllite
Fe
3+
2
(Si
 
4
O
 
10
)(OH)
 
2
14.19.6Greenalite
Fe
 
2-3
(Si
 
2
O
 
5
)(OH)
 
4
14.19.7Cronstedtite
Fe
2+
2
Fe
3+
 
((Si,Fe
3+
 
)
 
2
O
 
5
)(OH)
 
4
14.19.8Hisingerite
Fe
3+
2
(Si
 
2
O
 
5
)(OH)
 
4
 · 2H
 
2
O

Other Names for Fayalite

Synonyms:
Iron-Chrysolite
Other Languages:
Dutch:Fayaliet
German:Eisenglas
Eisenperidot
Faialit
Fayalit
Italian:Fayalite
Lithuanian:Fajalitas
Polish:Fajalit
Portuguese:Faialite
Russian:Фаялит
Simplified Chinese:铁橄榄石
Spanish:Faialita
Fayalita

Other Information

Health Warning:No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for Fayalite

Reference List:

- +
Gmelin, C.G. (1840): Chemische Untersuchung des Fayalites, Annalen der Chemie und Physik, Vol. 127 (2/051), pp. 160

von Fellenberg, R.L. (1840): Analyse des Eisenperidots, eines neuen vulkanischen Minerals von den Azoren, Annalen der Physik und Chemie, Vol. 127 (2/051), pp. 261

O'Neill, H.St.C. (1987): The quartz-fayalite-magnetite equilibria and free energies of formation of fayalite (Fe2SiO4) and magnetite (Fe3O4). American Mineralogist: 72: 67-75.

Mineralogical Magazine (1998): 62: 607.

Internet Links for Fayalite

Search Engines:
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  • Raman and XRD data at RRUFF project
  • American Mineralogist Crystal Structure Database
  • Fayalite details from Handbook of Mineralogy (PDF)
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