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Tephroite

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Formula:
Mn22+SiO4
System:
Orthorhombic
Colour:
Grey, olive-green, flesh ...
Lustre:
Vitreous, Greasy
Hardness:
6
Member of:
Name:
Named in 1823 by Johann Friedrich August Breithaupt from Greek τεφροζ "tephros" = ash-colored, alluding to the usual gray color of the mineral.

Classification of Tephroite

Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
9.AC.05

9 : SILICATES (Germanates)
A : Nesosilicates
C : Nesosilicates without additional anions; cations in octahedral [6] coordination
Dana 7th ed.:
51.3.1.4
51.3.1.4

51 : NESOSILICATES Insular SiO4 Groups Only
3 : Insular SiO4 Groups Only with all cations in octahedral [6] coordination
14.17.2

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

General Appearance of Type Material:
Unknown
Place of Conservation of Type Material:
Unknown
Year of Discovery:
1823

Occurrences of Tephroite

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

Physical Properties of Tephroite

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:
3.87 - 4.12 g/cm3 (Measured)    4.15 g/cm3 (Calculated)

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°
Max Birefringence:
δ = 0.101
Image 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:
Mn22+SiO4
Essential elements:
All elements listed in formula:
Analytical Data:
An analysis of the type material published by

Rammelsberg, C. F., (1843): Analysis of tephroite: Handbuch der Mineral-Chemie, 1st ed., 1st suppl., p.80, (Also in Poggendorff's Annalen (1844.), Band 62, p.137)
SiO2 (28.66)
MnO (68.88)
FeO (2.92)
100. 46
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:
Other Members of Group:
Calcio-olivineCa2SiO4
FayaliteFe22+SiO4
ForsteriteMg2SiO4
GlaucochroiteCaMn2+SiO4
KirschsteiniteCaFe2+SiO4
LaihuniteFe2+Fe23+(SiO4)2
Liebenbergite(Ni,Mg)2SiO4
MonticelliteCaMgSiO4
Olivine(Mg,Fe2+)2SiO4
Roepperite (of Brush)(Fe22+,Mn,Zn)SiO4
9.AC.05FayaliteFe22+SiO4
9.AC.05ForsteriteMg2SiO4
9.AC.05GlaucochroiteCaMn2+SiO4
9.AC.05KirschsteiniteCaFe2+SiO4
9.AC.05LaihuniteFe2+Fe23+(SiO4)2
9.AC.05Liebenbergite(Ni,Mg)2SiO4
9.AC.10MonticelliteCaMgSiO4
9.AC.15BrunogeieriteFe22+Ge4+O4
9.AC.15Ringwoodite(Mg,Fe2+)2SiO4
9.AC.20ChesnokoviteNa2[SiO2(OH)2] · 8H2O
14.17.1RhodoniteMnSiO3
14.17.3BrauniteMn2+Mn63+(SiO4)O8
14.17.4AlleghanyiteMn52+(SiO4)2(OH)2
14.17.5Ribbeite(Mn2+,Mg)5(SiO4)2(OH)2
14.17.6LeucophoeniciteMn72+(SiO4)3(OH)2
14.17.7JerrygibbsiteMn92+(SiO4)4(OH)2
14.17.8BementiteMn7Si6O15(OH)8
14.17.9Parsettensite(K,Na,Ca)7.5(Mn,Mg)49Si72O168(OH)50 · nH2O
14.17.10YofortieriteMn5Si8O20(OH)2 · 8-9H2O

Other Names for Tephroite

Name in Other Languages:
German:Tephroit
Simplified Chinese:锰橄榄石
Spanish:Tephroita
Traditional Chinese:錳橄欖石

Other Information

Health Risks:
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.

Rammelsberg, C. F., (1843): Analysis of tephroite: Handbuch der Mineral-Chemie, 1st ed., 1st suppl., p.80

Tjerk Peters, Hans Schwander, Volkmar Trommsdorff(1973):Assemblages among tephroite, pyroxmangite, rhodochrosite, quartz: Experimental data and occurrences in the Rhetic Alps. Contributions to Mineralogy and Petrology Volume 42, Issue 4, pp 325-332

Takei H (1976) Czochralski growth of Mn2SiO4 (tephroite) single crystal and its properties, Journal of Crystal Growth, 34, 125-131

H. D. Stidham , J. B. Bates , C. B. Finch (1976):Vibrational spectra of synthetic single crystal tephroite, Mn2SiO4. Journal of physical chemistry, Vol 80, pp 1226–1234

Francis C A, Ribbe P H (1980) The forsterite-tephroite series: I. crystal structure refinements, American Mineralogist, 65, 1263-1269

Fujino K, Sasaki S, Takéuchi Y, Sadanaga R (1981) X-ray determination of electron distributions in forsterite, fayalite and tephroite, Acta Crystallographica, B37, 513-518

Urusov V S, Lapina I V, Kravchuk I F, Kabalov Y K (1984) Isomorphism in the forsterite-tephroite series [in Russian], Geokhimiya, 7, 1047-1055

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

Urusov V S, Lapina I V, Kabalov Y K, Kravchuk I F (1985) Isomorphism in the forsterite-tephroite series [in English], Geochemistry International, 22, 80-88

Shannon, R. D. and Subramanian, M. A. and Hosoya, S. and Rossman, G. R. (1991) Dielectric Constants of Tephroite, Fayalite and Olivine
and the Oxide Additivity Rule. Physics and Chemistry of Minerals, 18 (1). pp. 1-6.

Redfern S A T, Knight K S, Henderson C M B, Wood B J (1998) Fe-Mn cation ordering in fayalite-tephroite (FexMn1-X)2SiO4 olivines: a neutron diffraction study, Mineralogical Magazine, 62, 607-615

Christoph Stüber and Wolfgang Laqua(1998): Point Defects of Tephroite. I: The Electrical Conductivity of Mn2SiO4. Zeitschrift für Physikalische Chemie, Vol 296, Pages 197–218

Mouri T, Enami M (2008) Raman spectroscopic study of olivine-group minerals, Journal of Mineralogical and Petrological Sciences, 103, 100-104

Chung-Cherng Lin and Chien-Chih Chen(2011): Elasticity of tephroite (α-Mn2SiO4) and a comparison of the elastic properties of silicate olivines. European Journal of Mineralogy v. 23, p. 35-43

Internet Links for Tephroite

Localities for Tephroite

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