Aenigmatite Mineral Data

Aenigmatite Mineral Data +

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General Aenigmatite Information

Chemical Formula:

Na2Fe++5TiSi6O20

Composition:

Molecular Weight = 861.60 gm

Sodium 5.34 % Na 7.19 % Na₂O

Titanium 5.56 % Ti 9.27 % TiO₂

Iron 32.41 % Fe 41.69 % FeO

Silicon 19.56 % Si 41.84 % SiO₂

Oxygen 37.14 % O

______ ______

100.00 % 100.00 % = TOTAL OXIDE

Empirical Formula:

Na₂Fe²⁺₅TiSi₆O₂₀

Environment:

A primary constituent in sodium-rich alkalic volcanics, pegmatites, and other silica-poor igneous rocks.

IMA Status:

Valid Species (Pre-IMA) 1865

Locality:

Notable studied occurrences include: at Naujakasik, near the Tunugdliarfik Fjord, and on the Kangerdluarssuk Plateau, in the Ilimaussaq intrusion; from Narssarssuk; and elsewhere in Gr Link to MinDat.org Location Data.

Name Origin:

From the Greek for riddle, apparently an allusion to its (formerly) uncertain chemical composition.

Synonym:

Cossyrite

ICSD 15283

PDF 46-1473

Aenigmatite Image

Images:

Aenigmatite

Comments: Dark, crystal prism of aenigmatite in white albite with astrophyllite.
Location: Mount Eveslogchorr, Khibiny Massif, Kola Peninsula, Murmansk District, Russia. Scale: See Photo.
© Jeff Weissman / Photographic Guide to Mineral Species

Aenigmatite Crystallography

Axial Ratios:

a:b:c =0.9623:1:0.8254

Cell Dimensions:

a = 10.406, b = 10.813, c = 8.926, Z = 2; alpha = 104.933°, beta = 96.866°, gamma = 128.316° V = 755.95 Den(Calc)= 3.78

Crystal System:

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

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

By Intensity(I/I_o): 3.14(1), 8.11(1), 2.705(0.8),

Crystal Structure:

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Cannillo E , Mazzi F , Fang J H , Robinson P D , Ohya Y , American Mineralogist , 56 (1971) p.427-446, The crystal structure of aenigmatite, sample CM

View Additional jPOWD Structure files for Aenigmatite
[1] [2] [3]

Physical Properties of Aenigmatite

Cleavage:

[???] Perfect

Color:

Brown, Black.

Density:

3.74 - 3.85, Average = 3.79

Diaphaniety:

Opaque

Habit:

Lamellar - Thin laminae producing a lamellar structure.

Hardness:

5-6 - Between Apatite and Orthoclase

Luminescence:

Non-fluorescent.

Luster:

Subadamantine

Streak:

reddish brown

Optical Properties of Aenigmatite

Gladstone-Dale:

CI meas= -0.013 (Superior) - where the CI = (1-KPDmeas/KC)
CI calc= -0.017 (Superior) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.2191,KPDmeas= 0.2183,KC= 0.2155

Optical Data:

Biaxial (+), a=1.78-1.8, b=1.8-1.82, g=1.87-1.9, bire=0.0900-0.1000, 2V(Calc)=56-60, 2V(Meas)=27-55. Dispersion single.

Pleochroism (x):

light brown.

Pleochroism (y):

brown.

Pleochroism (z):

dark brown.

Calculated Properties of Aenigmatite

Electron Density:

r_electron=3.68 gm/cc
note: r_Aenigmatite=3.80 gm/cc.

Fermion Index

Fermion Index = 0.02336
Boson Index = 0.97664

Photoelectric:

PE_Aenigmatite= 11.46 barns/electron
U=PE_Aenigmatite x r_electron= 42.21 barns/cc.

Radioactivity:

GRapi = 0 (Gamma Ray American Petroleum Institute Units)

Aenigmatite is Not Radioactive

Aenigmatite Classification

Dana Class:

69.2.1a.1 (69)Inosilicate Chains with Side Branches or Loops

(69.2)with P>2

(69.2.1a)Aenigmatite and related species (Aenigmatite subgroup)

69.2.1a.1 Aenigmatite Na2Fe5TiSi6O20 P1 1

69.2.1a.2 Dorrite Ca2Mg2Fe4(Al,Fe)4Si2O20 P1,P 1 Tri

69.2.1a.3 Hogtuvaite (Ca,Na)2(Fe,Fe,Ti,Mg,Mn)6(Si,Be,Al)6O20 P1 1

69.2.1a.4 Krinovite NaMg2CrSi3O10 P1 1

69.2.1a.5 Rhonite Ca2(Mg,Fe,Fe,Ti)6(Si,Al)6O20 P1 1

69.2.1a.6 Serendibite Ca2(Mg,Al)6(Si,Al,B)6O20 P1 1

69.2.1a.7 Welshite Ca2Mg4(Mn,Fe)Sb2O2[Si3Be2O18] P1 1

69.2.1a.8 Wilkinsonite Na2Fe4Fe2Si6O20 P1 1

69.2.1a.9 IMA2002-009a! Ca2Fe4FeTiSi4BeAlO20 P1 1

Strunz Class:

VIII/F.14-20 VIII - Silicates

VIII/F - Inosilicates (chain and band) modified double chains

VIII/F.14 - Aenigmatite group

VIII/F.14-10 Krinovite NaMg2CrSi3O10 P1 1

VIII/F.14-20 Aenigmatite Na2Fe5TiSi6O20 P1 1

VIII/F.14-30 Wilkinsonite Na2Fe4Fe2Si6O20 P1 1

VIII/F.14-35 Hogtuvaite (Ca,Na)2(Fe,Fe,Ti,Mg,Mn)6(Si,Be,Al)6O20 P1 1

VIII/F.14-40 Dorrite Ca2Mg2Fe4(Al,Fe)4Si2O20 P1,P 1 Tri

VIII/F.14-50 Rhonite Ca2(Mg,Fe,Fe,Ti)6(Si,Al)6O20 P1 1

VIII/F.14-60 Serendibite Ca2(Mg,Al)6(Si,Al,B)6O20 P1 1

VIII/F.14-70 Welshite Ca2Mg4(Mn,Fe)Sb2O2[Si3Be2O18] P1 1

Other Aenigmatite Information

References:

NAME( AntBidBlaNic2) PHYS. PROP.(Enc. of Minerals,2nd ed.,1990) OPTIC PROP.(Ford32)

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Aenigmatite

Na2Fe++5TiSi6O20
Dana No: 69.2.1a.1 Strunz No: VIII/F.14-20
Locality:

Notes: