Olmsteadite Mineral Data

Olmsteadite Mineral Data +

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General Olmsteadite Information

Chemical Formula:

KFe++2(Nb,Ta)(PO4)2O2·2(H2O)

Composition:

Molecular Weight = 523.68 gm

Potassium 7.47 % K 8.99 % K₂O

Tantalum 8.64 % Ta 10.55 % Ta₂O₅

Niobium 13.31 % Nb 19.03 % Nb₂O₅

Iron 21.33 % Fe 27.44 % FeO

Phosphorus 11.83 % P 27.11 % P₂O₅

Hydrogen 0.77 % H 6.88 % H₂O

Oxygen 36.66 % O

______ ______

100.00 % 100.00 % = TOTAL OXIDE

Empirical Formula:

KFe²⁺₂Nb_0.75Ta_0.25(PO₄)₂O₂·2(H₂O)

Environment:

Found in Nb-Ta bearing pegmatites.

IMA Status:

Approved IMA 1976

Locality:

Big Chief pegmatite, near Glendale, Pennington County, South Dakota, USA. Link to MinDat.org Location Data.

Name Origin:

Named for Milo Olmstead, micromount mineral collector, Rapid City, South Dakota, USA.

Synonym:

ICSD 12138

PDF 35-633

Olmsteadite Image

Images:

Olmsteadite

Comments: Dark brown crystals of olmsteadite with jahnsite on siderite.
Location: Big Chief mine, Keystone, Penningtion County, South Dakota, USA. Scale: Not Given.
© Lou Perloff / Photo Atlas of Minerals

Olmsteadite Crystallography

Axial Ratios:

a:b:c =0.7512:1:0.6492

Cell Dimensions:

a = 7.512, b = 10, c = 6.492, Z = 2; V = 487.68 Den(Calc)= 3.57

Crystal System:

Orthorhombic - PyramidalH-M Symbol (mm2) Space Group: Pb21m

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

By Intensity(I/I_o): 6.006(1), 3.003(0.7), 3.047(0.6),

Crystal Structure:

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Moore P B , Araki T , Kampf A R , Steele I M , American Mineralogist , 61 (1976) p.5-11, Olmstaedite, K2Fe2[Fe2(Nb,Ta)2O4(H2O)4(PO4)4], a new species, its crystal, structure and relation to vauxite and montgomeryite

Physical Properties of Olmsteadite

Cleavage:

[100] Good, [001] Good

Color:

Brown, Reddish brown, Black.

Density:

3.31 - 3.36, Average = 3.33

Diaphaniety:

Transparent to Translucent

Fracture:

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

Habit:

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

Hardness:

4 - Fluorite

Luster:

Subadamantine

Streak:

olive green

Optical Properties of Olmsteadite

Gladstone-Dale:

CI meas= -0.116 (Poor) - where the CI = (1-KPDmeas/KC)
CI calc= -0.042 (Good) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.218,KPDmeas= 0.2334,KC= 0.2091

Optical Data:

Biaxial (+), a=1.725-1.765, b=1.755-1.775, g=1.815-1.835, bire=0.0700-0.0900, 2V(Calc)=46-74, 2V(Meas)=60.

Pleochroism (x):

blue green.

Pleochroism (y):

yellow.

Pleochroism (z):

brown.

Calculated Properties of Olmsteadite

Electron Density:

r_electron=3.41 gm/cc
note: r_Olmsteadite=3.57 gm/cc.

Fermion Index

Fermion Index = 0.00471
Boson Index = 0.99529

Photoelectric:

PE_Olmsteadite= 120.73 barns/electron
U=PE_Olmsteadite x r_electron= 411.53 barns/cc.

Radioactivity:

GRapi = 102.84 (Gamma Ray American Petroleum Institute Units)

Estimated Radioactivity from Olmsteadite - barely detectable

Olmsteadite Classification

Dana Class:

42.7.11.1 (42)Hydrated Phosphates, etc., Containing Hydroxyl or Halogen

(42.7)where (AB)5 (XO4)3 Zq · x(H2O)

(42.7.11)Dana Group

42.7.11.1 Olmsteadite KFe2(Nb,Ta)(PO4)2O2·2(H2O) Pb21m mm2

42.7.11.2 Johnwalkite K(Mn,Fe,Fe)2(Nb,Ta)(PO4)2O2((H2O),OH)2 Pb21m mm2

Strunz Class:

VII/D.39-10 VII - Phosphates, Arsenates and Vanadates

VII/D - Water-bearing phosphates with unfamiliar anions, cations of very big and medium size: Al, Mg and Ca, Na, K

VII/D.39 - Olmsteadite - Johnwalkite series

VII/D.39-10 Olmsteadite KFe2(Nb,Ta)(PO4)2O2·2(H2O) Pb21m mm2

VII/D.39-20 Johnwalkite K(Mn,Fe,Fe)2(Nb,Ta)(PO4)2O2((H2O),OH)2 Pb21m mm2

Other Olmsteadite Information

References:

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

See Also:

Links to other databases for Olmsteadite :
1 -Am. Min. Crystal Structure Database 2 -Athena 3 - EUROmin Project 4 -Google Images 5 -Google Scholar 6 -Handbook of Mineralogy (UofA) 7 -MinDAT 8 -MinMax(Deutsch) 9 -MinMax(English) 10 -Mineralienatlas (Deutsch) 11 -QUT Mineral Atlas 12 - WWW-MINCRYST 13 -École des Mines de Paris

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

Olmsteadite

KFe++2(Nb,Ta)(PO4)2O2·2(H2O)
Dana No: 42.7.11.1 Strunz No: VII/D.39-10
Locality:

Notes: