Tweddillite Mineral Data

Tweddillite Mineral Data

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General Tweddillite Information

Chemical Formula:

CaSr(Mn+++,Fe+++)2Al[Si3O12](OH)

Composition:

Molecular Weight = 559.08 gm

Strontium 15.67 % Sr 18.53 % SrO

Calcium 7.17 % Ca 10.03 % CaO

Manganese 14.74 % Mn 21.18 % Mn₂O₃

Aluminum 6.27 % Al 11.85 % Al₂O₃

Iron 4.00 % Fe 5.71 % Fe₂O₃

Silicon 15.07 % Si 32.24 % SiO₂

Hydrogen 0.16 % H 1.45 % H₂O

Oxygen 36.92 % O

______ ______

100.00 % 101.00 % = TOTAL OXIDE

Empirical Formula:

CaSrMn³⁺_1.5Al_0.3Fe³⁺_0.4Al(Si₃O₁₂)(OH)_0.9

Environment:

Calc-silicate rocks formed by hydrothermal alteration of Mn ores. Epidote Group.

IMA Status:

Approved IMA 2002 (Dana # Added)

Locality:

Wessels mine, Kalahari manganese fields, South Africa. Link to MinDat.org Location Data.

Name Origin:

Named for Samuel M. Tweddill, first curator (1897 to 1915) of the Museum of the Geological Survey, Pretoria, Republic of South Africa.

Synonym:

IMA2001-014

Tweddillite Image

Images:

Tweddillite

Comments: Thin-section of (100) twinned tweddillite blades (red-orange-magenta ) in a matrix of serandite-pectolite (white-grey-yellow). Crossed polarizers. (MinMag 66:144).
Location: Kalahari manganese fields (Republic of South Africa). Scale: Picture Size 1 mm.
© Mineralogical Magazine

Tweddillite Crystallography

Axial Ratios:

a:b:c =1.5675:1:1.8094

Cell Dimensions:

a = 8.932, b = 5.698, c = 10.31, Z = 2; beta = 114.56° V = 477.25 Den(Calc)= 3.89

Crystal System:

Monoclinic - PrismaticH-M Symbol (2/m) Space Group: P 2₁/m

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

By Intensity(I/I_o): 2.936(1)(113), 2.182(0.8)(401), 2.586(0.8)(202),2.703(0.8)(300), 3.513(0.5)(211), 2.149(0.4)(221), 2.854(0.4)(020), 2.415(0.3),

Crystal Structure:

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Armbruster T , Gnos E , Dixon R , Gutzmer J , Hejny C , Dobelin N , Medenbach O , Mineralogical Magazine , 66 (2002) p.137-150, Manganvesuvianite and tweddillite, two new Mn3+-silicate minerals, from the Kalahari manganese fields, South Africa, Locality: Kalahari manganese fields, South Africa

Physical Properties of Tweddillite

Cleavage:

[001] Perfect

Color:

Deep red.

Diaphaniety:

Transparent

Fracture:

Brittle - Subconchoidal - Brittle frature with subconchoidal fragments

Habit:

Bladed - Aggregates of thin lath-like crystals (e.g. kyanite).

Habit:

Radial - Crystals radiate from a center without producing stellar forms (e.g. stibnite)

Hardness:

6-7 - Orthoclase-Quartz

Luster:

Vitreous (Glassy)

Streak:

brownish red

Optical Properties of Tweddillite

Gladstone-Dale:

CI calc= 0.062 (Fair) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.2121,KC= 0.2262

Optical Data:

Biaxial (+), b=1.825

Calculated Properties of Tweddillite

Electron Density:

r_electron=3.74 gm/cc
note: r_Tweddillite=3.89 gm/cc.

Fermion Index

Fermion Index = 0.01912
Boson Index = 0.98088

Photoelectric:

PE_Tweddillite= 23.90 barns/electron
U=PE_Tweddillite x r_electron= 89.44 barns/cc.

Radioactivity:

GRapi = 0 (Gamma Ray American Petroleum Institute Units)

Tweddillite is Not Radioactive

Tweddillite Classification

Dana Class:

58.2.1a.15 (58)Sorosilicate Insular, Mixed, Single, and Larger Tetrahedral Groups

(58.2)with cations in [6] and higher coordination; single and double groups (n=1,2)

(58.2.1a)Epidote group (Epidote subgroup)

58.2.1a.1 Allanite-(Ce) (Ce,Ca,Y)2(Al,Fe)3(SiO4)3(OH) P 2₁/m 2/m

58.2.1a.2 Allanite-(La)! Ca(REE,Ca)Al2(Fe,Fe)(SiO4)(Si2O7)O(OH) P 2₁/m 2/m

58.2.1a.3 Allanite-(Y) (Y,Ce,Ca)2(Al,Fe)3(SiO4)3(OH) P 2₁/m 2/m

58.2.1a.4 Clinozoisite Ca2Al3(SiO4)3(OH)=Ca2AlAl2(SiO4)(Si2O7)O(OH) P 2₁/m 2/m

58.2.1a.5 Dissakisite-(Ce) Ca(Ce,REE)(Mg,Fe)(Al,Fe)2Si3O12(OH) P 2₁/m 2/m

58.2.1a.6 Dollaseite-(Ce) CaCeMg2AlSi3O11(OH,F)2 P 2₁/m 2/m

58.2.1a.7 Epidote Ca2(Fe,Al)3(SiO4)3(OH)=Ca2(Fe,Al)Al2(SiO4)(Si2O7)O(OH) P 2₁/m 2/m

58.2.1a.8 Hancockite (Ca,Pb,Sr)2(Al,Fe)3(SiO4)(Si2O7)O(OH) P 2₁/m 2/m

58.2.1a.9 Khristovite-(Ce) (Ca,REE)(Ce,REE)(Mg,Fe,Cr,Ti,V,Al)MnAl(SiO4)(Si2O7)(OH)(F,O) P 2₁/m 2/m

58.2.1a.10 Mukhinite Ca2Al2V(SiO4)3(OH) P 2₁/m 2/m

58.2.1a.11 Piemontite Ca2(Al,Mn,Fe)3(SiO4)3(OH)=Ca2(Mn,Fe)Al2(SiO4)(Si2O7)O(OH) P 2₁/m 2/m

58.2.1a.12 Strontiopiemontite (Ca,Mn)(Sr,Ca)Mn(Al,Mn,Fe)2(SiO4)(Si2O7)O(OH) P 2₁/m 2/m

58.2.1a.13 Androsite-(La)! (Mn,Ca)(La,Ce,Ca,Nd)AlMnMn(SiO4)(Si2O7)O(OH) P 2₁/m 2/m

58.2.1a.14 Ferriallanite-(Ce)! CaCe(Fe,Fe,Al)3[SiO4][Si2O7]O(OH) P 2₁/m 2/m

58.2.1a.15 Tweddillite ! CaSr(Mn,Fe)2Al[Si3O12](OH) P 2₁/m 2/m

58.2.1a.16 Gatelite-(Ce)! (Ca,Ce,La,Nd)4(Al,Mg,Fe)4[Si2O7][SiO4]3(O,F,OH)3 P 2₁/a 2/m

58.2.1a.17 Niigataite! CaSrAl3(Si2O7)(SiO4)O(OH) P 2₁/m 2/m

58.2.1a.18 Vastmanlandite-(Ce)! Ce3CaMg2Al2Si5O19(OH)2F P 2₁/m 2/m

58.2.1a.19 IMA2002-049! (Mn,Ca)(Ce,REE)AlMnMn(Si2O7)(SiO4)O(OH) P 2₁/m 2/m

58.2.1a.20 Dissakisite-(La)! (Ca,Fe,Th)(REE,Ca)(Al,Cr,Ti)2(Mg,Fe,Al)Si3O12(OH,F)withLa>Ce P 2₁/m 2/m

58.2.1a.22 IMA2004-015! (Mn,Ca)(REE)VAlMn(Si2O7)(SiO4)O(OH) P 2₁/m 2/m

Strunz Class:

VIII/C.23-45 VIII - Silicates

VIII/C - Sorosilicates, mixed structure with [SiO4]2- "inseln" and [Si2O7]6- groups

VIII/C.23 - Epidote group

VIII/C.23-10 Clinozoisite Ca2Al3(SiO4)3(OH)=Ca2AlAl2(SiO4)(Si2O7)O(OH) P 2₁/m 2/m

VIII/C.23-20 Epidote Ca2(Fe,Al)3(SiO4)3(OH)=Ca2(Fe,Al)Al2(SiO4)(Si2O7)O(OH) P 2₁/m 2/m

VIII/C.23-30 Piemontite Ca2(Al,Mn,Fe)3(SiO4)3(OH)=Ca2(Mn,Fe)Al2(SiO4)(Si2O7)O(OH) P 2₁/m 2/m

VIII/C.23-40 Strontiopiemontite (Ca,Mn)(Sr,Ca)Mn(Al,Mn,Fe)2(SiO4)(Si2O7)O(OH) P 2₁/m 2/m

VIII/C.23-43 Niigataite! CaSrAl3(Si2O7)(SiO4)O(OH) P 2₁/m 2/m

VIII/C.23-45 Tweddillite CaSr(Mn,Fe)2Al[Si3O12](OH) P 2₁/m 2/m

VIII/C.23-50 Mukhinite Ca2Al2V(SiO4)3(OH) P 2₁/m 2/m

VIII/C.23-52 Androsite-(La)! (Mn,Ca)(La,Ce,Ca,Nd)AlMnMn(SiO4)(Si2O7)O(OH) P 2₁/m 2/m

VIII/C.23-55 Dollaseite-(Ce) CaCeMg2AlSi3O11(OH,F)2 P 2₁/m 2/m

VIII/C.23-58 Dissakisite-(Ce) Ca(Ce,REE)(Mg,Fe)(Al,Fe)2Si3O12(OH) P 2₁/m 2/m

VIII/C.23-60 Allanite-(Y) (Y,Ce,Ca)2(Al,Fe)3(SiO4)3(OH) P 2₁/m 2/m

VIII/C.23-65 Allanite-(La)! Ca(REE,Ca)Al2(Fe,Fe)(SiO4)(Si2O7)O(OH) P 2₁/m 2/m

VIII/C.23-80 Allanite-(Ce) (Ce,Ca,Y)2(Al,Fe)3(SiO4)3(OH) P 2₁/m 2/m

VIII/C.23-85a Ferriallanite-(Ce)! CaCe(Fe,Fe,Al)3[SiO4][Si2O7]O(OH) P 2₁/m 2/m

VIII/C.23-85 Khristovite-(Ce) (Ca,REE)(Ce,REE)(Mg,Fe,Cr,Ti,V,Al)MnAl(SiO4)(Si2O7)(OH)(F,O) P 2₁/m 2/m

VIII/C.23-87 Gatelite-(Ce)! (Ca,Ce,La,Nd)4(Al,Mg,Fe)4[Si2O7][SiO4]3(O,F,OH)3 P 2₁/a 2/m

VIII/C.23-90 Hancockite (Ca,Pb,Sr)2(Al,Fe)3(SiO4)(Si2O7)O(OH) P 2₁/m 2/m

VIII/C.23-100 Zoisite Ca2Al3(SiO4)3(OH)=Ca2AlAl2(SiO4)(Si2O7)O(OH) Pnmc 2/m 2/m 2/m

Other Tweddillite Information

References:

NAME( AmMin, Vol 88, p 253) PHYS. PROP.(AmMin, Vol 88, p 253) OPTIC PROP.(AmMin, Vol 88, p 253)

See Also:

Links to other databases for Tweddillite :
1 -Am. Min. Crystal Structure Database 2 -Athena 3 -Google Images 4 -Google Scholar 5 -MinDAT 6 -MinMax(Deutsch) 7 -MinMax(English) 8 -Mineralienatlas (Deutsch) 9 -QUT Mineral Atlas

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Print or Cut-and-Paste your Tweddillite Specimen Label here :

Tweddillite

CaSr(Mn+++,Fe+++)2Al[Si3O12](OH)
Dana No: 58.2.1a.15 Strunz No: VIII/C.23-45
Locality:

Notes: