Macfallite Mineral Data

Macfallite Mineral Data +

General Macfallite Information

Chemical Formula:

Ca2(Mn+++,Al)3(SiO4)(Si2O7)(OH)3

Composition:

Molecular Weight = 542.26 gm

Calcium 14.78 % Ca 20.68 % CaO

Manganese 25.33 % Mn 36.39 % Mn₂O₃

Aluminum 2.49 % Al 4.70 % Al₂O₃

Silicon 15.54 % Si 33.24 % SiO₂

Hydrogen 0.56 % H 4.98 % H₂O

Oxygen 41.31 % O

______ ______

100.00 % 100.00 % = TOTAL OXIDE

Empirical Formula:

Ca₂Mn³⁺_2.5Al_0.5(SiO₄)(Si₂O₇)(OH)₃

Environment:

Associated with other Mn-silicates.

IMA Status:

Approved IMA 1979

Locality:

Manganese Lake, Copper Harbor, Keweenaw County, Michigan, USA. Link to MinDat.org Location Data.

Name Origin:

Named for Russell P. MacFall, a dedicated amateur mineralogist.

Synonym:

ICSD 1612

PDF 42-601

Macfallite Image

Images:

Macfallite Johnsenite-(Ce) Braunite-I

Comments: Tiny - less than 1mm - maroon crystals of mcfallite suspended as inclusions in massive quartz along with larger spots of brown johnsenite-(Ce) and braunite.
Location: Artur mine, Jaguaracu, Minas Gerais, Brazil. Scale: Overall 3 x 2.5 slab.
© Tom Loomis / Dakota Matrix

Macfallite Crystallography

Axial Ratios:

a:b:c =1.6817:1:1.4738

Cell Dimensions:

a = 10.235, b = 6.086, c = 8.97, Z = 2; beta = 110.75° V = 522.50 Den(Calc)= 3.45

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): 3.399(1), 3.892(0.7), 2.962(0.5),

Crystal Structure:

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Moore P B , Shen J , Araki T , American Mineralogist , 70 (1985) p.171-181, Crystal chemistry of the (M2)3+ phi2 sheet: Structural principles and crystal, structures of ruizite, macfallite and orientite

Physical Properties of Macfallite

Cleavage:

[001] Perfect

Color:

Brown, Maroon, Reddish brown, Pink.

Density:

3.43

Habit:

Acicular - Occurs as needle-like crystals.

Habit:

Aggregates - Made of numerous individual crystals or clusters.

Habit:

Twinning Common - Crystals are usually twinned.

Hardness:

5-5.5 - Apatite-Knife Blade

Luster:

Vitreous - Silky

Streak:

brown

Optical Properties of Macfallite

Gladstone-Dale:

CI meas= 0.07 (Fair) - where the CI = (1-KPDmeas/KC)
CI calc= 0.075 (Fair) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.2301,KPDmeas= 0.2314,KC= 0.2488

Optical Data:

Biaxial (-), a=1.773-1.775, b=1.795, g=1.81-1.815, bire=0.0370-0.0400, 2V(Calc)=78-88, 2V(Meas)=86.

Pleochroism (x):

colorless or yellow.

Pleochroism (y):

light brown or light brown.

Pleochroism (z):

brownish red or dark brown.

Calculated Properties of Macfallite

Electron Density:

r_electron=3.37 gm/cc
note: r_Macfallite=3.43 gm/cc.

Fermion Index

Fermion Index = 0.00765
Boson Index = 0.99235

Photoelectric:

PE_Macfallite= 8.92 barns/electron
U=PE_Macfallite x r_electron= 30.03 barns/cc.

Radioactivity:

GRapi = 0 (Gamma Ray American Petroleum Institute Units)

Macfallite is Not Radioactive

Macfallite Classification

Dana Class:

58.2.3.2 (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)

(58.2.3)Sursassite and related species

58.2.3.1 Sursassite Mn2Al3(SiO4)(Si2O7)(OH)3 P 2₁/m 2/m

58.2.3.2 Macfallite Ca2(Mn,Al)3(SiO4)(Si2O7)(OH)3 P 2₁/m 2/m

Strunz Class:

VIII/C.24-10 VIII - Silicates

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

VIII/C.24 - Pumpellyite group

VIII/C.24-10 Macfallite Ca2(Mn,Al)3(SiO4)(Si2O7)(OH)3 P 2₁/m 2/m

VIII/C.24-20 Sursassite Mn2Al3(SiO4)(Si2O7)(OH)3 P 2₁/m 2/m

VIII/C.24-30 Pumpellyite-(Mg) Ca2MgAl2(SiO4)(Si2O7)(OH)2·(H2O) A2/m 2/m

VIII/C.24-40 Pumpellyite-(Fe++) Ca2Fe(Al,Fe)2(SiO4)(Si2O7)(OH)2·(H2O) A2/m 2/m

VIII/C.24-42 Pumpellyite-(Fe+++) Ca2FeAl2(SiO4)(Si2O7)(OH,O)2·(H2O) A2/m 2/m

VIII/C.24-50 Pumpellyite-(Mn++) Ca2(Mn,Mg)(Al,Mn,Fe)2(SiO4)(Si2O7(OH)2·(H2O) A2/m 2/m

VIII/C.24-60 Julgoldite-(Fe++) Ca2Fe(Fe,Al)2(SiO4)(Si2O7)(OH)2·(H2O) C 2/m 2/m

VIII/C.24-61 Julgoldite-(Fe+++) Ca2Fe(Fe,Al)2(SiO4)(Si2O7)(O,OH)2·(H2O) A2/m 2/m

VIII/C.24-70 Shuiskite Ca2(Mg,Al)(Cr,Al)2(SiO4)(Si2O7)(OH)2·(H2O) A2/m 2/m

VIII/C.24-80 Okhotskite-(Mg)* Ca3(Mg,Mn)(Mn,Al,Fe)(SiO4)(Si2O7)(OH)2·(H2O) Mono

VIII/C.24-80* Okhotskite-(Mn++) Ca2(Mn,Mg)(Mn,Al,Fe)Si3O10(OH)4 A2/m 2/m

VIII/C.24-90 Samfowlerite Ca14Mn3Zn2(Be,Zn)2Be6(SiO4)6(Si2O7)4(OH,F)6 P 2₁/c 2/m

Other Macfallite Information

References:

NAME( Dana8) PHYS. PROP.(Dana8) OPTIC PROP.(Dana8)

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Macfallite

Ca2(Mn+++,Al)3(SiO4)(Si2O7)(OH)3
Dana No: 58.2.3.2 Strunz No: VIII/C.24-10
Locality:

Notes: