Tephroite Mineral Data

Tephroite Mineral Data +

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General Tephroite Information

Chemical Formula:

Mn2SiO4

Composition:

Molecular Weight = 201.96 gm

Manganese 54.41 % Mn 70.25 % MnO

Silicon 13.91 % Si 29.75 % SiO₂

Oxygen 31.69 % O

______ ______

100.00 % 100.00 % = TOTAL OXIDE

Empirical Formula:

Mn²⁺₂(SiO₄)

Environment:

Contact metamorphism of manganese bearing rocks.

IMA Status:

Valid Species (Pre-IMA) 1823

Locality:

Franklin and Sparta, New Jersey, USA. Link to MinDat.org Location Data.

Name Origin:

From the Greek tephros - "ash gray" for its color.

Synonym:

ICSD 100433

PDF 35-748

Tephroite Image

Images:

Tephroite

Comments: Sharp crystals of tephroite to 1.2 cm across.
Location: N'Chwaning Mine, Kalahari Manganese Field, Northern Cape Province, South Africa. Scale: Picture size 5 cm.
© John Veevaert

Images:

Tephroite Ericssonite Orthoericssonite

Comments: Dark brown ericssonite, intergrown with orthoericssonite, with pink rhodonite, light brown diopside (var. schefferite) and gray tephroite.
Location: Langban, Varmland, Sweden. Scale: See Photo.
© Jeff Weissman / Photographic Guide to Mineral Species

Images:

Tephroite Johnbaumite

Comments: Violet crystalline massive johnbaumite with brown tephroite.
Location: Jacobsberg, Varmland, Sweden. Scale: See Photo.
© Jeff Weissman / Photographic Guide to Mineral Species

Tephroite 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)= 4.62

Crystal System:

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

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

By Intensity(I/I_o): 2.56(1), 2.86(0.85), 3.61(0.85),

Crystal Structure:

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Francis C A , Ribbe P H , American Mineralogist , 65 (1980) p.1263-1269, The forsterite-tephroite series: I. Crystal structure refinements, Te 91, olivine

Physical Properties of Tephroite

Cleavage:

[010] Indistinct

Color:

Gray, Olive green, Bluish green, Red, Reddish brown.

Density:

4.11 - 4.39, Average = 4.25

Diaphaniety:

Transparent to translucent

Fracture:

Brittle - Conchoidal - Very brittle fracture producing small, conchoidal fragments.

Habit:

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

Habit:

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

Habit:

Prismatic - Crystals Shaped like Slender Prisms (e.g. tourmaline).

Hardness:

6.5 - Pyrite

Luminescence:

None.

Luster:

Vitreous - Greasy

Magnetism:

Nonmagnetic

Streak:

gray

Optical Properties of Tephroite

Gladstone-Dale:

CI meas= 0.054 (Good) - where the CI = (1-KPDmeas/KC)
CI calc= 0.13 (Poor) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.1743,KPDmeas= 0.1895,KC= 0.2003

Optical Data:

Biaxial (+), a=1.759, b=1.797, g=1.86, bire=0.1010, 2V(Calc)=78, 2V(Meas)=60-70. Dispersion none.

Pleochroism (x):

pale amber.

Pleochroism (y):

orange yellow.

Pleochroism (z):

pale amber.

Calculated Properties of Tephroite

Electron Density:

r_electron=4.04 gm/cc
note: r_Tephroite=4.25 gm/cc.

Fermion Index

Fermion Index = 0.00664
Boson Index = 0.99336

Photoelectric:

PE_Tephroite= 14.67 barns/electron
U=PE_Tephroite x r_electron= 59.28 barns/cc.

Radioactivity:

GRapi = 0 (Gamma Ray American Petroleum Institute Units)

Tephroite is Not Radioactive

Tephroite Classification

Dana Class:

51.3.1.4 (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.04-30 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 Tephroite Information

References:

NAME( Duda&Rejl90) PHYS. PROP.(Enc. of Minerals,2nd ed.,1990) OPTIC PROP.(Mason68)

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Tephroite

Mn2SiO4
Dana No: 51.3.1.4 Strunz No: VIII/A.04-30
Locality:

Notes: