Coombsite Mineral Data

General Coombsite Information

Chemical Formula:

K(Mn++,Fe++,Mg)13(Si,Al)18O42(OH)14

Composition:

Molecular Weight = 2,127.66 gm

Potassium 1.84 % K 2.21 % K₂O

Magnesium 1.49 % Mg 2.46 % MgO

Manganese 20.14 % Mn 26.01 % MnO

Aluminum 5.71 % Al 10.78 % Al₂O₃

Iron 10.24 % Fe 13.17 % FeO

Silicon 17.82 % Si 38.12 % SiO₂

Hydrogen 0.66 % H 5.93 % H₂O

Oxygen 42.11 % O

______ ______

100.00 % 98.68 % = TOTAL OXIDE

Empirical Formula:

KMn²⁺_7.8Fe²⁺_3.9Mg_1.3Si_13.5Al_4.5O₄₂(OH)₁₄

IMA Status:

Approved IMA 1996 (Dana # Added)

Locality:

Watson's Beach, Otago, South Island, New Zealand Link to MinDat.org Location Data.

Name Origin:

Named for D.S Coombs of the University of Otago, New Zealand.

Synonym:

IMA1989-058

Coombsite Image

Images:

Coombsite

Comments: Sawed slab with brownish veining in pink (?) matrix.
Location: Watson's Beach, Otago, South Island,, New Zealand. Scale: 3x2cm x 5mm.
© Tom Loomis / Dakota Matrix

Coombsite Crystallography

Axial Ratios:

a:c = 1:2.46415

Cell Dimensions:

a = 11.828, c = 29.146, Z = 3; V = 3,531.28 Den(Calc)= 3.00

Crystal System:

Trigonal Space Group: R 3 or R 3

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

By Intensity(I/I_o): 9.68(1), 2.556(0.9), 2.793(0.7),

Physical Properties of Coombsite

Cleavage:

{???} Good

Color:

Brown.

Density:

Diaphaneity:

Translucent

Luster:

Vitreous (Glassy)

Streak:

brownish yellow

Optical Properties of Coombsite

Gladstone-Dale:

CI meas= 0.019 (Superior) - where the CI = (1-KPDmeas/KC)
CI calc= 0.019 (Superior) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.2032,KPDmeas= 0.2032,KC= 0.207
Ncalc = 1.62

Optical Data:

Uniaxial (-), e=1.6, w=1.619, bire=0.0190.

Calculated Properties of Coombsite

Electron Density:

Bulk Density (Electron Density)=2.93 gm/cc
note: Specific Gravity of Coombsite =3.00 gm/cc.

Fermion Index:

Fermion Index = 0.01
Boson Index = 0.99

Photoelectric:

PE_Coombsite= 9.23 barns/electron
U=PE_Coombsite x r_electron= 27.08 barns/cc.

Radioactivity:

GRapi = 25.94 (Gamma Ray American Petroleum Institute Units)
Concentration of Coombsite per GRapi unit = 3.85 (%)

Estimated Radioactivity from Coombsite - barely detectable

Coombsite Classification

Dana Class:

74.01.04.02 (74)Phyllosilicate Modulated Layers

(74.01)with joined islands

(74.01.04)Dana Group

74.01.04.01 Zussmanite K(Fe,Mg,Mn)13[AlSi17O42](OH)14 R 3 3

74.01.04.02 Coombsite! K(Mn,Fe,Mg)13(Si,Al)18O42(OH)14 R 3 or R 3 Trig

Strunz Class:

09.EG.35 09 - SILICATES (Germanates)

09.E - Phyllosilicates

09.EG -Double nets with 6-membered and larger rings

09.EG.35 Coombsite! K(Mn,Fe,Mg)13(Si,Al)18O42(OH)14 R 3 or R 3 Trig

09.EG.35 Zussmanite K(Fe,Mg,Mn)13[AlSi17O42](OH)14 R 3 3

Other Coombsite Information

References:

PHYS. PROP.(37th List of New Min.,Min. Mag.,1996) OPTIC PROP.(37th List of New Min.,Min. Mag.,19)

See Also:

Links to other databases for Coombsite :
1 - Am. Min. Crystal Structure Database
2 - Athena
3 - EUROmin Project
4 - Ecole des Mines de Paris
5 - GeoScienceWorld
6 - Google Images
7 - Google Scholar
8 - Handbook of Mineralogy (MinSocAm)
9 - Handbook of Mineralogy (UofA)
10 - MinDAT
11 - Mineralienatlas (Deutsch)
12 - Online Mineral Museum
13 - QUT Mineral Atlas
14 - Ruff.Info

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

Coombsite

K(Mn++,Fe++,Mg)13(Si,Al)18O42(OH)14
Dana No: 74.01.04.02 Strunz No: 09.EG.35
Locality:

Notes:

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