Cryptomelane Mineral Data

General Cryptomelane Information

Chemical Formula:

K(Mn++++,Mn++)8O16

Composition:

Molecular Weight = 734.59 gm

Potassium 5.32 % K 6.41 % K₂O

Manganese 59.83 % Mn 19.31 % MnO / 71.01 % MnO₂

Oxygen 34.85 % O

______ ______

100.00 % 96.73 % = TOTAL OXIDE

Empirical Formula:

KMn⁴⁺₆Mn²⁺₂O₁₆

Environment:

Commonest of the hard, black, fine-grained manganese oxides formerly called psilomelane.

IMA Status:

Valid Species (Pre-IMA) 1942

Locality:

Chindwara, India. Link to MinDat.org Location Data.

Name Origin:

From the Greek for hidden and black, as the identity of this common, black mineral is lost in the group of other black Mn-bearing oxides.

Name Pronunciation:

Cryptomelane + Pronunciation

Synonym:

Psilomelane

Cryptomelane Image

Images:

Click Here for Larger Cryptomelane Image

Cryptomelane Adamite

Comments: Black, rounded balls of cryptomelane and purple, transparent adamite.
Location: Ojuela mine, Mapimi, Druango, Mexico. Scale: Not Given.
© Lou Perloff / Photo Atlas of Minerals

Cryptomelane Crystallography

Axial Ratios:

a:b:c =3.3993:1:3.4513

Cell Dimensions:

a = 9.79, b = 2.88, c = 9.94, Z = 1; beta = 90.62° V = 280.24 Den(Calc)= 4.35

Crystal System:

Monoclinic - PrismaticH-M Symbol (2/m) Space Group: I2/m

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

By Intensity(I/I_o): 2.399(1), 1.654(0.8), 3.11(0.8),

Crystal Structure:

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drag2 - RMB Resize/Rotate
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Help on Above

Post J E , Von Dreele R B , Buseck P R , Acta Crystallographica, Section B , 38 (1982) p.1056-1065, Symmetry and cation displacements in hollandites:, structure refinements of hollandite, cryptomelane and priderite, Locality: Chindwara, India, Note: -1M polytype, Note: Anisotropic displacement factors from ICSD

Physical Properties of Cryptomelane

Color:

Black, Gray, Blue gray.

Density:

4.36

Diaphaneity:

Opaque

Fracture:

Conchoidal - Fractures developed in brittle materials characterized by smoothly curving surfaces, (e.g. quartz).

Habit:

Botryoidal - "Grape-like" rounded forms (e.g.. malachite).

Habit:

Cryptocrystalline - Occurs as crystals too small to distinguish with the naked eye.

Habit:

Massive - Uniformly indistinguishable crystals forming large masses.

Hardness:

6-6.5 - Orthoclase-Pyrite

Luster:

Sub Metallic

Streak:

brownish black

Optical Properties of Cryptomelane

Optical Data:

NCalc= 2.44 - from Gladstone-Dale relationship (KC = 0.3304) where Ncalc=Dcalc*KC+1
NCalc= 2.44 - from Gladstone-Dale relationship (KC = 0.3304) where Ncalc=Dmeas*KC+1

Calculated Properties of Cryptomelane

Electron Density:

Bulk Density (Electron Density)=4.11 gm/cc
note: Specific Gravity of Cryptomelane =4.35 gm/cc.

Fermion Index:

Fermion Index = 0.0001736569
Boson Index = 0.9998263431

Photoelectric:

PE_Cryptomelane= 16.25 barns/electron
U=PE_Cryptomelane x r_electron= 66.76 barns/cc.

Radioactivity:

GRapi = 72.57 (Gamma Ray American Petroleum Institute Units)
Concentration of Cryptomelane per GRapi unit = 1.38 (%)

Estimated Radioactivity from Cryptomelane - barely detectable

Cryptomelane Classification

Dana Class:

07.09.01.02 (07)Multiple Oxides

(07.09)Dana Type

(07.09.01)Cryptomelane Group (Hard black, fine-grained)

07.09.01.01 Hollandite Ba(Mn,Mn)8O16 I2/m 2/m

07.09.01.02 Cryptomelane K(Mn,Mn)8O16 I2/m 2/m

07.09.01.03 Manjiroite (Na,K)(Mn,Mn)8O16•n(H2O) I 4/m 4/m

07.09.01.04 Coronadite Pb(Mn,Mn)8O16 I2/m 2/m

07.09.01.05 Strontiomelane! SrMn6Mn2O16 P 2₁/m 2/m

07.09.01.06 Henrymeyerite! BaFeTi7O16 I 4/m 4/m

Strunz Class:

04.DK.10 04 - OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodate

04.D - Metal:Oxygen = 1:2 and similar

04.DK -With large (± medium-sized) cations; tunnel structures

04.DK.10 Cryptomelane K(Mn,Mn)8O16 I2/m 2/m

04.DK.10 Todorokite (Na,Ca,K)2(Mn,Mn)6O12•3-4.5(H2O) P 2/m 2/m

04.DK.10 Romanechite (Ba,H2O)2(Mn,Mn)5O10 C 2/m 2/m

04.DK.10 Strontiomelane! SrMn6Mn2O16 P 2₁/m 2/m

Other Cryptomelane Information

References:

NAME( Dana8) PHYS. PROP.(Enc. of Minerals,2nd ed.,1990)

See Also:

Links to other databases for Cryptomelane :
1 - Am. Min. Crystal Structure Database
2 - Athena
3 - Ecole des Mines de Paris
4 - Franklin Minerals(Dunn)
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
15 - WWW-MINCRYST
16 - theimage

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Ask about Cryptomelane here :
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Mindat.org's Discussion Groups
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Print or Cut-and-Paste your Cryptomelane Specimen Label here :

Cryptomelane

K(Mn++++,Mn++)8O16
Dana No: 07.09.01.02 Strunz No: 04.DK.10
Locality:

Notes: