Sewardite Mineral Data

General Sewardite Information

Chemical Formula:

CaFe+++2(AsO4)2(OH)2

Composition:

Molecular Weight = 464.68 gm

Calcium 8.62 % Ca 12.07 % CaO

Zinc 1.41 % Zn 1.75 % ZnO

Iron 22.83 % Fe 32.65 % Fe₂O₃

Arsenic 32.25 % As 49.46 % As₂O₅

Hydrogen 0.46 % H 4.07 % H₂O

Oxygen 34.43 % O

______ ______

100.00 % 100.00 % = TOTAL OXIDE

Empirical Formula:

CaFe³⁺_1.9Zn_0.1(AsO₄)₂(OH)_1.9(H₂O)_0.1

Environment:

Intergrown with ferrilotharmeyerite and another unknown. (Ca-dominant analogue of carminite; structure)

IMA Status:

Approved IMA 2002 (Dana # Added)

Locality:

31st Level, Tsumeb mine, Tsumeb, Namibia. Link to MinDat.org Location Data.

Name Origin:

Named for Terry Maxwell Seward (1940-) who collected the mineral.

Synonym:

IMA2001-054

Sewardite Image

Images:

Sewardite

Comments: Photomicrograph of an isolated fragment of red sewardite as well as a fragment in green to black botryoidal matrix.
Location: Single specimen of gangue collected from the 31st level of the Tsumeb mine, Tsumeb, Namibia. Scale: See Image.
© Canadian Mineralogist

Images:

Sewardite

Comments: Deep red, micaceous sewardite crystals mistakenly identified as carminite.
Location: Benjamin Hill, Sonora, Mexico. Scale: Picture size 1 cm.
© Tom Loomis / Dakota Matrix

Sewardite Crystallography

Axial Ratios:

a:b:c =2.2142:1:1.6318

Cell Dimensions:

a = 16.461, b = 7.434, c = 12.131, Z = 8; V = 1,484.48 Den(Calc)= 4.16

Crystal System:

Orthorhombic - DipyramidalH-M Symbol (2/m 2/m 2/m) Space Group: C ccm

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

By Intensity(I/I_o): 3.167(1)(022), 2.503(0.9)(422,314), 4.874(0.9)(202),2.919(0.7)(511), 3.389(0.6)(220), 1.775(0.5)(026), 2.988(0.5)(313), 3.015(0.5)(510), 3.473(0.5)(113),

Crystal Structure:

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Roberts A C , Cooper M A , Hawthorne F C , Criddle A J , Stirling J A R , The Canadian Mineralogist , 40 (2002) p.1191-1198, Sewardite, CaFe2(AsO4)(OH)2, the Ca-analogue of carminite,, from Tsumeb, Namibia: Description and crystal structure, Locality: Tsumeb, Namibia

Physical Properties of Sewardite

Cleavage:

{100} Imperfect, {011} Imperfect

Color:

Dark red, Lighter red orange.

Diaphaneity:

Translucent

Fracture:

Splintery - Thin, elongated fractures produced by intersecting good cleavages or partings (e.g. hornblende).

Habit:

Aggregates - Made of numerous individual crystals or clusters.

Habit:

Anhedral Grains - Granular minerals without the expression of crystal shapes

Habit:

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

Hardness:

3.5 - Copper Penny

Luster:

Vitreous (Glassy)

Streak:

reddish brown

Optical Properties of Sewardite

Optical Data:

NCalc= 1.94 - from Gladstone-Dale relationship (KC = 0.2249) where Ncalc=Dcalc*KC+1

RL Anisotrophism:

None.

RL Bireflectance:

Weak.

RL Color:

Light bluish gray with bright pink to red internal reflections.

RL Pleochroism:

None.

Reflectivity

**Standardized Intensity (100%) Reflection Spectra of Sewardite in Air**
λ	R₁	R₂	∑ R₁(λ)	∑ R₂(λ)
460 nm	10.12	10.71
540 nm	9.53	10.07
580 nm	9.30	9.98
640 nm	8.99	9.66

**Calculated Relative Intensity Colors of Sewardite in Air**
Relative Intensity	0%	100%	200%	300%	400%	500%	600%	700%	800%	900%	950%
R₁
R₂

Calculated Properties of Sewardite

Electron Density:

Bulk Density (Electron Density)=3.95 gm/cc
note: Specific Gravity of Sewardite =4.16 gm/cc.

Fermion Index:

Fermion Index = 0.0057003424
Boson Index = 0.9942996576

Photoelectric:

PE_Sewardite= 30.83 barns/electron
U=PE_Sewardite x rElectron Density= 121.72 barns/cc.

Radioactivity:

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

Sewardite Classification

Dana Class:

41.10.06.02 (41)Anhydrous Phosphates, etc. Containing Hydroxyl or Halogen

(41.10)where (A++ B++)3 (XO4)2 Zq

(41.10.06)Carminite Group

41.10.06.01 Carminite PbFe2(AsO4)2(OH)2 C ccm 2/m 2/m 2/m

41.10.06.02 Sewardite! CaFe2(AsO4)2(OH)2 C ccm 2/m 2/m 2/m

Strunz Class:

08.BH.30 08 - PHOSPHATES, ARSENATES, VANADATES

08.B - Phosphates, etc. with Additional Anions, without H2O

08.BH -With medium-sized and large cations, (OH,etc.):RO4 = 1:1

08.BH.30 Carminite PbFe2(AsO4)2(OH)2 C ccm 2/m 2/m 2/m

08.BH.30 Sewardite! CaFe2(AsO4)2(OH)2 C ccm 2/m 2/m 2/m

Other Sewardite Information

References:

NAME( AmMin, v 88, p 1178) PHYS. PROP.(AmMin, v 88, p 1178) OPTIC PROP.(AmMin, v 88, p 1178)

See Also:

Links to other databases for Sewardite :
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 Sewardite using:

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Ask about Sewardite here :
Ask-A-Mineralogist from the Mineralogical Society of America
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 Sewardite Specimen Label here :

Sewardite

CaFe+++2(AsO4)2(OH)2
Dana No: 41.10.06.02 Strunz No: 08.BH.30
Locality:

Notes: