Cummingtonite Mineral Data

Cummingtonite Mineral Data

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General Cummingtonite Information

Chemical Formula:

[ ]Mg7Si8O22(OH)2

Composition:

Molecular Weight = 780.82 gm

Magnesium 21.79 % Mg 36.13 % MgO

Silicon 28.78 % Si 61.56 % SiO₂

Hydrogen 0.26 % H 2.31 % H₂O

Oxygen 49.18 % O

______ ______

100.00 % 100.00 % = TOTAL OXIDE

Empirical Formula:

Mg₇(Si₈O₂₂)(OH)₂

Environment:

Contact and regional metamorphic rocks.

IMA Status:

Valid Species (Pre-IMA) 1824

Locality:

Cummington, Massachusetts, USA. Link to MinDat.org Location Data.

Name Origin:

Named after its locality.

Synonym:

ICSD 81355

PDF 42-545

Cummingtonite Image

Images:

Cummingtonite

Comments: Light brown prismatic crystalline aggregate of cummingtonite with radiating structure.
Location: West Chesterfield, Hampshire County, Massachusetts, USA. Scale: See Photo.
© Jeff Weissman / Photographic Guide to Mineral Species

Cummingtonite Crystallography

Axial Ratios:

a:b:c =0.5229:1:0.292

Cell Dimensions:

a = 9.534, b = 18.231, c = 5.3235, Z = 2; beta = 101.97° V = 905.18 Den(Calc)= 2.86

Crystal System:

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

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

By Intensity(I/I_o): 8.33(1), 2.756(0.7), 3.06(0.7),

Crystal Structure:

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Fischer K F , American Mineralogist , 51 (1966) p.814-818, A further refinement of the crystal structure of cummingtonite, (Mg,Fe)7(Si4O11)2(OH)2

View Additional jPOWD Structure files for Cummingtonite
[1] [10] [11] [12] [13] [2] [3] [4] [5] [6] [7] [8] [9]

Physical Properties of Cummingtonite

Cleavage:

[110] Perfect, [???] Distinct

Color:

White, Black, Blackish brown, Blackish green, Gray.

Density:

3.1 - 3.6, Average = 3.35

Diaphaniety:

Transparent to translucent to opaque

Fracture:

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

Habit:

Columnar - Forms columns

Habit:

Fibrous - Crystals made up of fibers.

Habit:

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

Hardness:

5-6 - Between Apatite and Orthoclase

Luminescence:

Non-fluorescent.

Luster:

Vitreous - Silky

Streak:

grayish white

Optical Properties of Cummingtonite

Gladstone-Dale:

CI meas= 0.04 (Good) - where the CI = (1-KPDmeas/KC)
CI calc= -0.125 (Poor) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.2341,KPDmeas= 0.1999,KC= 0.2082

Optical Data:

Biaxial (+), a=1.639-1.671, b=1.647-1.689, g=1.664-1.708, bire=0.0250-0.0370, 2V(Calc)=70-90, 2V(Meas)=65-90. Dispersion r > v or r < v.

Pleochroism (x):

colorless, colorless, or pale yellow.

Pleochroism (y):

colorless, pale yellow, or pale brown.

Pleochroism (z):

colorless, pale greenish yellow, or pale violet.

Calculated Properties of Cummingtonite

Electron Density:

r_electron=3.35 gm/cc
note: r_{Cummingtonite}=3.35 gm/cc.

Fermion Index

Fermion Index = 0.03546
Boson Index = 0.96454

Photoelectric:

PE_{Cummingtonite}= 1.59 barns/electron
U=PE_{Cummingtonite} x r_electron= 5.33 barns/cc.

Radioactivity:

GRapi = 0 (Gamma Ray American Petroleum Institute Units)

Cummingtonite is Not Radioactive

Cummingtonite Classification

Dana Class:

66.1.1.2 (66)Inosilicate Double-Width Unbranched Chains, W=2

(66.1)Dana Type

(66.1.1)Group 1, the Mg-Fe-Mn-Li amphiboles (Monoclinic)

66.1.1.1 Magnesiocummingtonite (Mg,Fe)7Si8O22(OH)2 C 2/m 2/m

66.1.1.2 Cummingtonite []Mg7Si8O22(OH)2 C 2/m 2/m

66.1.1.3 Grunerite []Fe7Si8O22(OH)2 C 2/m 2/m

66.1.1.3b Permanganogrunerite! []Mn4(Fe)3(Si8O22)(OH)2 C 2/m 2/m

66.1.1.4 Manganocummingtonite Na(Na,Mn)2(Mg4,Fe)5Si8O22(OH)2 C 2/m 2/m

66.1.1.5 Manganogrunerite []Mn2Fe5Si8O22(OH) C 2/m 2/m

66.1.1.6 Magnesioclinoholmquistite? Li2(Mg,Fe)3Al2Si8O22(OH)2 C 2/m 2/m

66.1.1.7 Clinoholmquistite? [](Li2Mg3Al2)Si8O22(OH)2 C 2/m 2/m

66.1.1.8 Clinoferroholmquistite [](Li2Fe3Al2)Si8O22(OH)2 C 2/m 2/m

66.1.1.8a Ferri-clinoholmquistite! []Li2Mg3(Fe3)2(Si8O22)(OH)2 C 2/m 2/m

66.1.1.8b Ferri-clinoferroholmquistite! []Li2(Fe2Fe3)Si8O22(OH)2 C 2/m 2/m

66.1.1.9 Sodic-ferripedrizite! Na(LiNa)(Fe2Mg2Li)Si8O22(OH,F)2 C 2/m 2/m

66.1.1.9a Ferripedrizite! NaLi2(Fe2Mg2Li)Si8O22(OH)2 C 2/m 2/m

66.1.1.9b Sodic-ferri-ferropedrizite! NaLi2(Fe2Fe3)Si8O22(OH)2 C 2/m 2/m

66.1.1.9c Fluoro-sodic-pedrizite! NaLi2(Mg2Al2Li)S5Si8O22F2 C 2/m 2/m

Strunz Class:

VIII/F.07-20 VIII - Silicates

VIII/F - Inosilicates (chain and band) double chains [Si4O11]6- , Mg-Fe-Mn-Amphiboles

VIII/F.07 - Amphibole group, Magnesiocummingtonite - Ferroclinoholmquistite series

VIII/F.07-10 Magnesiocummingtonite (Mg,Fe)7Si8O22(OH)2 C 2/m 2/m

VIII/F.07-20 Cummingtonite []Mg7Si8O22(OH)2 C 2/m 2/m

VIII/F.07-30 Grunerite []Fe7Si8O22(OH)2 C 2/m 2/m

VIII/F.07-40 Manganocummingtonite Na(Na,Mn)2(Mg4,Fe)5Si8O22(OH)2 C 2/m 2/m

VIII/F.07-50 Manganogrunerite []Mn2Fe5Si8O22(OH) C 2/m 2/m

VIII/F.07-55 Permanganogrunerite! []Mn4(Fe)3(Si8O22)(OH)2 C 2/m 2/m

VIII/F.07-60 Magnesioclinoholmquistite? Li2(Mg,Fe)3Al2Si8O22(OH)2 C 2/m 2/m

VIII/F.07-70 Clinoholmquistite? [](Li2Mg3Al2)Si8O22(OH)2 C 2/m 2/m

VIII/F.07-80 Clinoferroholmquistite [](Li2Fe3Al2)Si8O22(OH)2 C 2/m 2/m

VIII/F.07-90 Ferri-clinoferroholmquistite! []Li2(Fe2Fe3)Si8O22(OH)2 C 2/m 2/m

Other Cummingtonite Information

References:

NAME( Duda&Rejl90) PHYS. PROP.(Enc. of Minerals,2nd ed.,1990) OPTIC PROP.(Heinrich65)

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

Cummingtonite

[ ]Mg7Si8O22(OH)2
Dana No: 66.1.1.2 Strunz No: VIII/F.07-20
Locality:

Notes: