Stilpnomelane Mineral Data

Stilpnomelane Mineral Data +

General Stilpnomelane Information

Chemical Formula:

K(Fe++,Mg,Fe+++)8(Si,Al)12(O,OH)27·n(H2O)

Composition:

Molecular Weight = 1,235.84 gm

Potassium 2.21 % K

Magnesium 2.75 % Mg

Aluminum 4.37 % Al

Iron 29.83 % Fe

Silicon 22.73 % Si

Hydrogen 0.57 % H

Oxygen 37.54 % O

______

100.00 %

Empirical Formula:

K_0.7Fe²⁺_3.3Mg_1.4Fe³⁺_3.3Si₁₀Al₂O₂₄(OH)₃·2(H₂O)

Environment:

Commonly associated with iron ores.

IMA Status:

Valid Species (Pre-IMA) 1827

Locality:

Moravia of Czechoslovakia at Sternberg in a bed of limonite. Link to MinDat.org Location Data.

Name Origin:

From the Greek for "shining" and "black", in allusion to its luster and color.

Synonym:

Ferristilpnomelane-high Fe+++

Ferrostilpnomelane-low Fe+++

Stilpnomelane Image

Images:

Stilpnomelane

Comments: Golden metallic scaly stilpnomelane on pink orthoclase.
Location: French Creek No. 2 Mine, near Saint Peters, Chester County, Pennsylvania, USA. Scale: See Photo.
© Jeff Weissman / Photographic Guide to Mineral Species

Stilpnomelane Crystallography

Axial Ratios:

a:b:c =1:1:0.8033

Cell Dimensions:

a = 22.2, b = 22.2, c = 17.835, Z = 9; alpha = 125.03°, beta = 95.98°, gamma = 120° V = 6,199.34 Den(Calc)= 2.98

Crystal System:

Triclinic - PinacoidalH-M Symbol ( 1) Space Group: P1

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

By Intensity(I/I_o): 2.55(1), 4.16(1), 12.3(1),

Physical Properties of Stilpnomelane

Cleavage:

[001] Perfect

Color:

Brown red, Green, Golden brown, Black.

Density:

2.77 - 2.96, Average = 2.86

Diaphaniety:

Subtranslucent to opaque

Fracture:

Brittle - Generally displayed by glasses and most non-metallic minerals.

Habit:

Fibrous - Crystals made up of fibers.

Habit:

Foliated - Two dimensional platy forms.

Habit:

Platy - Sheet forms (e.g. micas).

Hardness:

3 - Calcite

Luminescence:

Non-fluorescent.

Luster:

Vitreous - Dull

Streak:

gray white

Optical Properties of Stilpnomelane

Optical Data:

Biaxial (-), a=1.543-1.634, b=1.576-1.745, g=1.576-1.745, bire=0.0330-0.1110, 2V(Calc)=0, 2V(Meas)=0-40. Dispersion none.

Pleochroism (x):

pale yellow, golden yellow, pale brown, or colorless.

Pleochroism (y):

deep brown, nearly black, chestnut brown, deep yellowish brown, or light greenish yellow.

Pleochroism (z):

deep brown, nearly black, chestnut brown, deep yellowish brown, or light greenish yellow.

Calculated Properties of Stilpnomelane

Electron Density:

r_electron=2.93 gm/cc
note: r_{Stilpnomelane}=2.98 gm/cc.

Fermion Index

Fermion Index = 0.01987
Boson Index = 0.98013

Photoelectric:

PE_{Stilpnomelane}= 10.10 barns/electron
U=PE_{Stilpnomelane} x r_electron= 29.56 barns/cc.

Radioactivity:

GRapi = 31.37 (Gamma Ray American Petroleum Institute Units)

Estimated Radioactivity from Stilpnomelane - barely detectable

Stilpnomelane Classification

Dana Class:

74.1.1.1 (74)Phyllosilicate Modulated Layers

(74.1)with joined islands

(74.1.1)Stilpnomelane group

74.1.1.1 Stilpnomelane K(Fe,Mg,Fe)8(Si,Al)12(O,OH)27·n(H2O) P1 1

74.1.1.2 Lennilenapeite K6-7(Mg,Mn,Fe,Fe,Zn)48(Si,Al)72(O,OH)216·16(H2O) Unk (pseudo-HEX) Tri

74.1.1.3 Franklinphilite (K,Na)4(Mn,Mg,Zn)48(Si,Al)72(O,OH)216·6(H2O) pseudo-HEX P1 or P1 Tri

74.1.1.4 Bannisterite KCa(Mn,Fe,Zn,Mg)21(Si,Al)32O76(OH)16·4-12(H2O) A2/a 2/m

Strunz Class:

VIII/H.17-40 VIII - Silicates

VIII/H - Phyllosilicates (layered) Mica like layered silicates with [Si4O10]4- and related groups

VIII/H.17 - Stilpnomelane series

VIII/H.17-10 Bannisterite KCa(Mn,Fe,Zn,Mg)21(Si,Al)32O76(OH)16·4-12(H2O) A2/a 2/m

VIII/H.17-20 Bariumbannisterite* (K,H3O)(Ba,Ca)(Mn,Fe,Mg)21(Si,Al)32O80(O,OH)16·4-12(H2O) Mono

VIII/H.17-30 Lennilenapeite K6-7(Mg,Mn,Fe,Fe,Zn)48(Si,Al)72(O,OH)216·16(H2O) Unk (pseudo-HEX) Tri

VIII/H.17-40 Stilpnomelane K(Fe,Mg,Fe)8(Si,Al)12(O,OH)27·n(H2O) P1 1

VIII/H.17-45 Franklinphilite (K,Na)4(Mn,Mg,Zn)48(Si,Al)72(O,OH)216·6(H2O) pseudo-HEX P1 or P1 Tri

VIII/H.17-50 Parsettensite (K,Na,Ca)(Mn,Al)7Si8O20(OH)8·2(H2O)(?) C 2/m 2/m

VIII/H.17-60 Ganophyllite (K,Na)2(Mn,Al,Mg)8(Si,Al)12O29(OH)7·8-9(H2O) A2/a 2/m

VIII/H.17-70 Eggletonite Na2Mn8[Si11AlO29](OH)7·11(H2O) Ia or I2/a Mono

VIII/H.17-75 Tamaite! (Ca,K,Ba,Na)3-4Mn24(Si,Al)40(O,OH)112·21(H2O) P 2₁/a 2/m

VIII/H.17-80 Ekmanite? (Fe,Mg,Mn,Fe)3(Si,Al)4O10(OH)2·2(H2O) Unk Ortho

Other Stilpnomelane Information

References:

NAME( Ford32) PHYS. PROP.(Enc. of Minerals,2nd ed.,1990) OPTIC PROP.(Enc. of Minerals,2nd ed.,1990)

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Stilpnomelane

K(Fe++,Mg,Fe+++)8(Si,Al)12(O,OH)27·n(H2O)
Dana No: 74.1.1.1 Strunz No: VIII/H.17-40
Locality:

Notes: