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Fayalite

Big Photo

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

Show Fayalite Photos (30)
Formula:
Fe
2+
2
[SiO
 
4
]
System:OrthorhombicColour:Greenish-yellow, yellow ...
Lustre:Vitreous, GreasyHardness:7
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.

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)
Related to:
  • Olivine Group
    • 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
    CaMg[SiO
     
    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
    Fe
     
    2
    		[SiO
     
    3
    		]
     
    2
    14.19.3Laihunite
    Fe
    2+
     
    		Fe
    3+
    2
    		[SiO
     
    4
    		]
     
    2
    14.19.4Ferro-anthophyllite
    ☐[Fe
    2+
    2
    		][Fe
    2+
    5
    		][(OH)
     
    2
    		|Si
     
    8
    		O
     
    22
    		]
    14.19.5Ferripyrophyllite
    Fe
     
    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
    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

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  • Raman and XRD data at RRUFF project
  • American Mineralogist Crystal Structure Database
  • Search for Fayalite in the Natural History Museum (London) online catalogue
  • Fayalite details from Handbook of Mineralogy (PDF)
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  • Wright's Rock Shop - excellent mineral specimens since 1970
  • Find Fayalite on www.crystalclassics.co.uk
  • Rare and Unusual minerals at Mineralogical Research Company
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    Localities for Fayalite

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