Griffithite Mineral Data

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General Griffithite Information

Chemical Formula:

4(Mg,Fe,Ca)O.(Al,Fe)2O3.5SiO2•7(H2O)

Composition:

Molecular Weight = 764.30 gm

Calcium 2.10 % Ca 2.93 % CaO

Magnesium 7.63 % Mg 12.66 % MgO

Aluminum 5.30 % Al 10.01 % Al₂O₃

Iron 12.42 % Fe 11.28 % FeO / 5.22 % Fe₂O₃

Silicon 18.37 % Si 39.31 % SiO₂

Hydrogen 1.85 % H 16.50 % H₂O

Oxygen 52.33 % O

______ ______

100.00 % 97.91 % = TOTAL OXIDE

Empirical Formula:

Mg_2.4Fe²⁺_1.2Ca_0.4Al_1.5Fe³⁺_0.5Si₅O₁₈·7(H₂O)

Environment:

Amygdaloidal cavities in basalt. A variety of ferroan saponite.

IMA Status:

Not Approved IMA

Locality:

Cahuenga Pass, Griffith Park, Los Angeles, California, USA. Link to MinDat.org Location Data.

Name Origin:

Named after its locality.

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Images:

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Griffithite Crystallography

Crystal System:

Monoclinic

Physical Properties of Griffithite

Cleavage:

{001} Perfect

Color:

Dark green.

Density:

2.31

Diaphaneity:

Subtransparent to subtranslucent

Habit:

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

Hardness:

1 - Talc

Luminescence:

Non-fluorescent.

Luster:

Vitreous - Dull

Magnetism:

Magnetic after heating

Streak:

green

Optical Properties of Griffithite

Gladstone-Dale:

CI meas= -0.028 (Excellent) - where the CI = (1-KPDmeas/KC)
KPDmeas= 0.2341,KC= 0.2277
Ncalc = 1.53

Optical Data:

Biaxial (-), a=1.485, b=1.565, g=1.572, bire=0.0870

Pleochroism (x):

pale yellow.

Pleochroism (y):

olive green.

Pleochroism (z):

brownish green.

Calculated Properties of Griffithite

Electron Density:

Bulk Density (Electron Density)=2.32 gm/cc
note: Specific Gravity of Griffithite =2.31 gm/cc.

Fermion Index:

Fermion Index = 0.01
Boson Index = 0.99

Photoelectric:

PE_Griffithite= 4.93 barns/electron
U=PE_Griffithite x rElectron Density= 11.46 barns/cc.

Radioactivity:

GRapi = 0 (Gamma Ray American Petroleum Institute Units)
Griffithite is Not Radioactive

Griffithite Classification

Dana Class:

71.00.00.00 (71)Phyllosilicate Minerals

(71.00)Without Dana Classification Numbers

(71.00.00)Chlorite Group

71.00.00.00 Bariumbannisterite* (K,H3O)(Ba,Ca)(Mn,Fe,Mg)21(Si,Al)32O80(O,OH)16•4-12(H2O) Mono

71.00.00.00 Ekmanite? (Fe,Mg,Mn,Fe)3(Si,Al)4O10(OH)2•2(H2O) Unk Ortho

71.00.00.00 Griffithite* 4(Mg,Fe,Ca)O.(Al,Fe)2O3.5SiO2•7(H2O) Mono

71.00.00.00 Orlovite KLi2TiSi4O11F C 2 2

71.00.00.00 Shlykovite KCa[Si4O9(OH)]•3H2O P 2₁/c 2/m

71.00.00.00 Spodiophyllite? (Na,K)4(Mg,Fe)3(Fe,Al)2(Si8O24) Mono

71.00.00.00 Voloshinite Rb(LiAl1.5[]0.5)(Al0.5Si3.5)O10F2 C 2/c 2/m

Strunz Class:

09.EC.45 09 - SILICATES (Germanates)

09.E - Phyllosilicates

09.EC -Phyllosilicates with mica sheets, composed of tetrahedral and octahedral nets

09.EC.45 Griffithite* 4(Mg,Fe,Ca)O.(Al,Fe)2O3.5SiO2•7(H2O) Mono

09.EC.45 Hectorite Na0,3(Mg,Li)3Si4O10(OH)2 C 2/m 2/m

09.EC.45 Swinefordite (Li,Ca0.5,Na)0.72(Li,Al,Mg)2.66(Si,Al)4O10(OH,F)2•2(H2O) C 2/m (MON or ORTH) 2/m

09.EC.45 Zincsilite Zn3Si4O10(OH)2•4(H2O)(?) C 2/m ? 2/m

09.EC.45 Saponite (Ca/2,Na)0,3(Mg,Fe)3(Si,Al)4O10(OH)2•4(H2O) C 2/m 2/m

09.EC.45 Sauconite Na0,3Zn3(Si,Al)4O10(OH)2•4(H2O) C 2/m 2/m

09.EC.45 Spadaite MgSiO2(OH)2•(H2O)(?) Ortho

09.EC.45 Sobotkite? (K,Ca0.5)0.33(Mg,Al)3(Si3Al)O10(OH)2•1-5(H2O) Unk. Mono

09.EC.45 Stevensite (Ca0.5,Na)0.33(Mg,Fe)3Si4O10(OH)2•n(H2O) Unk (ORTH ?) Mono

09.EC.45 Ferrosaponite! Ca0.3(Fe,Mg,Fe)3(Si,Al)4O10(OH)2•4(H2O) C? Mono

Other Griffithite Information

References:

NAME( Ford32) PHYS. PROP.(Dana) OPTIC PROP.(Ford32)

See Also:

Links to other databases for Griffithite :
1 - Am. Min. Crystal Structure Database
2 - Athena
3 - GeoScienceWorld
4 - Google Images
5 - Google Scholar
6 - MinDAT
7 - Mineralienatlas (Deutsch)
8 - Online Mineral Museum
9 - QUT Mineral Atlas
10 - Ruff.Info

Search for Griffithite using:

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Ask about Griffithite here :
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Mindat.org's Discussion Groups
Original Rockhounds Discussion Group
Rockhounds Discussion Group on Yahoo Groups
Mineral Discussion Forum from Fabre Minerals - also available in Español

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

Griffithite

4(Mg,Fe,Ca)O.(Al,Fe)2O3.5SiO2•7(H2O)
Dana No: 71.00.00.00 Strunz No: 09.EC.45
Locality:

Notes: