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Tephroite

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Big Photo

Pumice quarries, Wingertsberg, Niedermendig, Mendig, Laach lake volcanic complex, Eifel, Rhineland-Palatinate, Germany
© C.H.M.-Schäfer

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Formula:
Mn
2+
2
SiO
 
4
System:OrthorhombicColour:Grey, olive-green, flesh ...
Lustre:Vitreous, GreasyHardness:6
Member of:Olivine Group
Name:From Greek "tephros", ash-colored, alluding to the usual gray colour of the mineral.


Olivine Group. Fayalite-Tephroite Series, and the Forsterite-Tephroite Series. The Mn2+ analogue of Fayalite, Forsterite, and Calcio-Olivine.

Classification of Tephroite

IMA status:Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
Strunz 8th edition ID:8/A.04-30
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 7th edition ID:51.3.1.4
Dana 8th edition ID:51.3.1.4

51 : NESOSILICATES Insular SiO4 Groups Only
3 : Insular SiO4 Groups Only with all cations in octahedral [6] coordination
Hey's CIM Ref.:14.17.2

14 : Silicates not Containing Aluminum
17 : Silicates of Mn
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Type Occurrence of Tephroite

Type Locality:Sterling Mine, Sterling Hill, Ogdensburg, Franklin Mining District, Sussex Co., New Jersey, USA
Year of Discovery:1823

Occurrences of Tephroite

Geological Setting:In Fe-Mn ore deposits, skarns, and metamorphosed manganese rich sediments.

Physical Properties of Tephroite

Lustre:Vitreous, Greasy
Diaphaneity (Transparency):Translucent
Colour:Grey, olive-green, flesh red or reddish-brown, dark brown.
Streak:Pale gray
Hardness (Mohs):6
Tenacity:Brittle
Cleavage:Distinct/Good
Distinct on {010}
Imperfect on {001}
Fracture:Irregular/Uneven, Conchoidal
Density (measured):3.87 - 4.12 g/cm3
Density (calculated):4.15 g/cm3

Crystallography of Tephroite

Crystal System:Orthorhombic
Class (H-M):mmm (2/m 2/m 2/m) - Dipyramidal
Cell Parameters:a = 4.88(2) Å, b = 10.61(2) Å, c = 6.24(2) Å
Ratio:a:b:c = 0.46 : 1 : 0.588
Unit Cell Volume:V 323.09 ų (Calculated from Unit Cell)
Z:4
Morphology:Short prismatic
Twinning:Uncommon {011}

Optical Data of Tephroite

Type:Biaxial (-)
RI values: nα = 1.759 nβ = 1.797 nγ = 1.860
2V:Measured: 60° to 70°, Calculated: 78°
Maximum Birefringence:δ = 0.101

Chart shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:Very High
Dispersion:r > v
Pleochroism:Weak
Comments:X= brownish red
Y= reddish
Z= greenish blue

Chemical Properties of Tephroite

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

Relationship of Tephroite to other Species

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

- +
Calcio-Olivine
Ca
 
2
SiO
 
4
Fayalite
Fe
2+
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
Related Minerals - Nickel-Strunz Grouping):

- +
9.AC.05Fayalite
Fe
2+
2
SiO
 
4
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.10Monticellite
CaMgSiO
 
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:

- +
14.17.1Rhodonite
MnSiO
 
3
14.17.3Braunite
Mn
2+
 
Mn
3+
6
(SiO
 
4
)O
 
8
14.17.4Alleghanyite
Mn
2+
5
(SiO
 
4
)
 
2
(OH)
 
2
14.17.5Ribbeite
(Mn
2+
 
,Mg)
 
5
(SiO
 
4
)
 
2
(OH)
 
2
14.17.6Leucophoenicite
Mn
2+
7
(SiO
 
4
)
 
3
(OH)
 
2
14.17.7Jerrygibbsite
Mn
2+
9
(SiO
 
4
)
 
4
(OH)
 
2
14.17.8Bementite
Mn
 
7
Si
 
6
O
 
15
(OH)
 
8
14.17.9Parsettensite
K
 
1.2
Mn
 
8
(Si,Al)
 
12
O
 
26
(OH)
 
10
14.17.10Yofortierite
Mn
 
5
Si
 
8
O
 
20
(OH)
 
2
 · 8-9H
 
2
O

Other Names for Tephroite

Synonyms:
Mangan-Peridot
Other Languages:
German:Tephroit
Russian:Тефроит
Simplified Chinese:锰橄榄石
Spanish:Tephroita

Other Information

Special Storage/
Display Requirements from:
Sterling Mine,..., Sussex Co., New Jersey, USANone.
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 Tephroite

Reference List:

- +
Breithaupt, A. (1823): Vollständige Charakteristik des Mineral-Systems.- Dresden, 2nd. ed., p. 278.

American Mineralogist (1980): 65: 1263-1269.

Francis, C.A. (1985) New data on the forsterite-tephroite series. American Mineralogist: 70: 568-575.

Mineralogical Magazine (1998): 63: 607.

Internet Links for Tephroite

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  • Raman and XRD data at RRUFF project
  • American Mineralogist Crystal Structure Database
  • Tephroite details from Handbook of Mineralogy (PDF)
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    • Localities for Tephroite

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    Locality Updated: Bolcana Mine, Deva, Hunedoara Co., RomaniaFrom David Von Bargen, 25th May 2013 18:32:39