Neptunite Mineral Data

Neptunite Mineral Data +

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General Neptunite Information

Chemical Formula:

KNa2Li(Fe++,Mn)2Ti2Si8O24

Composition:

Molecular Weight = 907.69 gm

Potassium 4.31 % K 5.19 % K₂O

Sodium 5.07 % Na 6.83 % Na₂O

Lithium 0.76 % Li 1.65 % Li₂O

Titanium 10.55 % Ti 17.60 % TiO₂

Manganese 3.03 % Mn 3.91 % MnO

Iron 9.23 % Fe 11.87 % FeO

Silicon 24.75 % Si 52.96 % SiO₂

Oxygen 42.30 % O

______ ______

100.00 % 100.00 % = TOTAL OXIDE

Empirical Formula:

KNa₂LiFe²⁺_1.5Mn²⁺_0.5Ti₂Si₈O₂₄

IMA Status:

Valid Species (Pre-IMA) 1893

Locality:

Benitoite mine, San Benito, Co., California, USA. Link to MinDat.org Location Data.

Name Origin:

Named for Neptune, the Roman god of the sea, because it was found with aegirine, named for the Scandinavian god of the sea.

Synonym:

Carlosite

ICSD 71360

PDF 43-677

Neptunite Image

Images:

Neptunite Natrolite

Comments: Jet-black square prisms of neptunite etched out of the enclosing white natrolite with minor benitoite.
Location: Benitoite Gem Mine. San Benito Co. California, USA. Scale: 6.5 x 6 cm.
© Fabre Minerals

Neptunite Crystallography

Axial Ratios:

a:b:c =1.3167:1:0.8008

Cell Dimensions:

a = 16.46, b = 12.5, c = 10.01, Z = 4; beta = 115.4° V = 1,860.47 Den(Calc)= 3.24

Crystal System:

Monoclinic - DomaticH-M Symbol (m) Space Group: Cc

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

By Intensity(I/I_o): 3.186(1), 9.6(0.6), 3.517(0.45),

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Crystal Structure:

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Kunz M , Armbruster T , Lager G A , Schultz A J , Goyette R J , Lottermoser W , Amthauer G , Physics and Chemistry of Minerals , 18 (1991) p.199-213, Fe, Ti ordering and octahedral distortions in acentric neptunite:, temperature dependent X-ray and neutron structure refinements, and Mossbauer Spectroscopy, Sample: T = 15 K

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

Physical Properties of Neptunite

Cleavage:

[110] Good

Color:

Black, Red.

Density:

3.23

Diaphaniety:

Translucent

Fracture:

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

Habit:

Crystalline - Coarse - Occurs as well-formed coarse sized crystals.

Habit:

Prismatic - Crystals Shaped like Slender Prisms (e.g. tourmaline).

Habit:

Tabular - Form dimensions are thin in one direction.

Hardness:

5-6 - Between Apatite and Orthoclase

Luminescence:

Non-fluorescent.

Luster:

Vitreous (Glassy)

Streak:

brown

Optical Properties of Neptunite

Gladstone-Dale:

CI meas= 0.081 (Poor) - where the CI = (1-KPDmeas/KC)
CI calc= 0.084 (Poor) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.2175,KPDmeas= 0.2182,KC= 0.2375

Optical Data:

Biaxial (+), a=1.69-1.6908, b=1.6927-1.7, g=1.7194-1.736, bire=0.0294-0.0452, 2V(Calc)=36-56, 2V(Meas)=36-49. Dispersion r < v strong.

Pleochroism (x):

yellow orange.

Pleochroism (y):

orange.

Pleochroism (z):

deep red.

Calculated Properties of Neptunite

Electron Density:

r_electron=3.16 gm/cc
note: r_Neptunite=3.23 gm/cc.

Fermion Index

Fermion Index = 0.02793
Boson Index = 0.97207

Photoelectric:

PE_Neptunite= 6.71 barns/electron
U=PE_Neptunite x r_electron= 21.19 barns/cc.

Radioactivity:

GRapi = 60.73 (Gamma Ray American Petroleum Institute Units)

Estimated Radioactivity from Neptunite - barely detectable

Neptunite Classification

Dana Class:

70.4.1.1 (70)Inosilicate Column or Tube Structures

(70.4)with linked chains forming cages

(70.4.1)Neptunite group

70.4.1.1 Neptunite KNa2Li(Fe,Mn)2Ti2Si8O24 Cc m

70.4.1.2 Mangan-neptunite KNa2Li(Mn,Fe)2Ti2Si8O24 C 2/m 2/m

70.4.1.3 Watatsumiite! Na2KMn2LiV2Si8O24 Cc m

Strunz Class:

VIII/F.37-10 VIII - Silicates

VIII/F - Inosilicates (chain and band) complex chain structure. Cylindric chains and others

VIII/F.37 - Neptunite series

VIII/F.37-10 Neptunite KNa2Li(Fe,Mn)2Ti2Si8O24 Cc m

VIII/F.37-20 Mangan-neptunite KNa2Li(Mn,Fe)2Ti2Si8O24 C 2/m 2/m

VIII/F.37-30 Watatsumiite! Na2KMn2LiV2Si8O24 Cc m

Other Neptunite Information

References:

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

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Neptunite

KNa2Li(Fe++,Mn)2Ti2Si8O24
Dana No: 70.4.1.1 Strunz No: VIII/F.37-10
Locality:

Notes: