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Strengite

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Johann August Streng
Formula:
FePO4 · 2H2O
System:
Orthorhombic
Colour:
Purple, violet, pink, ...
Hardness:
3½ - 4
Member of:
Name:
Named after Johann August Streng [February 4, 1830 Frankfort, Germany - January 7, 1897 Giessen, Germany], Professor of Mineralogy, University of Giessen, Germany. Streng was an assistant to Robert Bunsen at University of Heidelberg and later professor of chemistry at the Clausthal Mining Academy. Streng was an innovator in new methods of chemical titration.

Classification of Strengite

Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
8.CD.10

8 : PHOSPHATES, ARSENATES, VANADATES
C : Phosphates without additional anions, with H2O
D : With only medium-sized cations, RO4:H2O = 1:2
40.4.1.2

40 : HYDRATED NORMAL PHOSPHATES,ARSENATES AND VANADATES
4 : (AB)5(XO4)2·xH2O
19.13.2

19 : Phosphates
13 : Phosphates of Fe alone
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First Recorded Occurrence of Strengite

Year of Discovery:
1877
Geological Setting of First Recorded Material:
Phosphate-bearing iron ore deposit

Occurrences of Strengite

Geological Setting:
Secondary mineral formed under surface or near-surface conditions by the alteration of iron-bearing phosphates, such as Triphylite in pegmatite, or Dufrenite, or may occur in limonite ore deposits and gossans, magnetite iron ores, late-stage mineralization in granite pegmatites, or rarely as a cave mineral.

Physical Properties of Strengite

Vitreous, Sub-Vitreous, Greasy
Diaphaneity (Transparency):
Transparent, Translucent
Colour:
Purple, violet, pink, peach-blossom-red, carmine, greenish white, colorless; Colourless to pale pink in transmitted light.
Comment:
Usually lght pink
Streak:
white
Hardness (Mohs):
3½ - 4
Tenacity:
Brittle
Cleavage:
Distinct/Good
Good on {010}, poor on {001}
Density:
2.84 - 2.87 g/cm3 (Measured)    2.84 g/cm3 (Calculated)

Crystallography of Strengite

Crystal System:
Orthorhombic
Class (H-M):
mmm (2/m 2/m 2/m) - Dipyramidal
Space Group:
Pbca
Space Group Setting:
Pbca
Cell Parameters:
a = 8.7233(7) Å, b = 9.886(1) Å, c = 10.122(1) Å
Ratio:
a:b:c = 0.882 : 1 : 1.024
Unit Cell Volume:
V 872.91 ų
Z:
8
Morphology:
Crystals rarely octahedral {111}; usually thick to thin tabular {001}; also stout prismatic [100] or [010]. May be lathlike, radial fibrous, botyroidal or spherical aggregates and crusts.
Twinning:
Rarely on {201}

Crystallographic forms of Strengite

Crystal Atlas:
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Strengite no.1 - Goldschmidt (1913-1926)
Strengite no.3 - Goldschmidt (1913-1926)
3d models and HTML5 code kindly provided by www.smorf.nl.

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Transparency
Opaque | Translucent | Transparent

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X-Ray Powder Diffraction Data:
d-spacingIntensity
5.509 (60)
4.383 (85)
3.996 (45)
3.114 (100)
3.002 (45)
2.949 (45)
2.546 (50)
Comments:
ICDD 33-667

Optical Data of Strengite

Type:
Biaxial (+)
RI values:
nα = 1.697 - 1.708 nβ = 1.708 - 1.719 nγ = 1.741 - 1.745
2V:
Calculated: 72° to 88°
Birefringence:
0.044
Max Birefringence:
δ = 0.044
Image shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:
High
Dispersion:
relatively strong r < v
Pleochroism:
Non-pleochroic

Chemical Properties of Strengite

Formula:
FePO4 · 2H2O
Essential elements:
All elements listed in formula:
Common Impurities:
Al

Relationship of Strengite to other Species

Series:
Forms a series with Variscite (see here)
Forms a series with Scorodite (see here)
Member of:
Other Members of Group:
MansfielditeAlAsO4 · 2H2O
ScoroditeFe3+AsO4 · 2H2O
VarisciteAlPO4 · 2H2O
YanomamiteInAsO4 · 2H2O
8.CD.05KolbeckiteScPO4 · 2H2O
8.CD.05MetavarisciteAlPO4 · 2H2O
8.CD.05PhosphosideriteFePO4 · 2H2O
8.CD.05UM2005-02-AsO:AlHPScSiScAsO4 · 2H2O
8.CD.10MansfielditeAlAsO4 · 2H2O
8.CD.10ScoroditeFe3+AsO4 · 2H2O
8.CD.10VarisciteAlPO4 · 2H2O
8.CD.10YanomamiteInAsO4 · 2H2O
8.CD.15ParascoroditeFeAsO4 · 2H2O
8.CD.20Ludlamite(Fe,Mn,Mg)3(PO4)2 · 4H2O
8.CD.25SterlinghilliteMn3(AsO4)2 · 4H2O
8.CD.30RollanditeCu3(AsO4)2 · 4H2O
19.13.1BarbosaliteFe2+Fe23+(PO4)2(OH)2
19.13.3PhosphosideriteFePO4 · 2H2O
19.13.4DufréniteCa0.5Fe2+Fe53+(PO4)4(OH)6 · 2H2O
19.13.5GiniiteFe2+Fe43+(PO4)3(OH)5 · 2H2O
19.13.6WhitmoreiteFe2+Fe23+(PO4)2(OH)2 · 4H2O
19.13.7TinticiteFe3+5.34(PO4)3.62(VO4)0.38(OH)4 · 6.7H2O
19.13.8FerristrunziteFe3+Fe23+(PO4)2(OH)3 · 5H2O
19.13.9FerrostrunziteFe2+Fe23+(PO4)2(OH)2 · 6H2O
19.13.10BerauniteFe2+Fe53+(PO4)4(OH)5 · 6H2O
19.13.11VivianiteFe32+(PO4)2 · 8H2O
19.13.12MetavivianiteFe2+Fe23+(PO4)2(OH)2 · 6H2O

Other Names for Strengite

Name in Other Languages:
German:Strengit
Simplified Chinese:红磷铁矿
Spanish:Strengita
Traditional Chinese:紅磷鐵礦

Other Information

Not fluorescent in UV
Other Information:
Soluble in HCl but not in HNO3.
Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for Strengite

Reference List:
Zepharovich (1867) Konigliche Akademie der Wissenschaften, Vienna, Sitzber.: 56: 20 (as Barrandite).

Nies (1877) Neues Jahrbuch für Mineralogie, Geologie und Paleontologie, Heidelberg, Stuttgart: 8-16.

Schaller, Waldemar Theodore (1913), The refractive indices of strengite: Journal of the Washington Academy of Science: 3: 249.

Laubmann and Steinmetz (1920) Zeitschrift für Kristallographie, Mineralogie und Petrographie, Leipzig: 55: 542-546.

Goldschmidt, V. (1922) Atlas der Krystallformen. 9 volumes, atlas, and text: vol. 8: 89.

de Jesus (1935) Com. Serv. Geol. Portugal: 19: 65.

Himmel and Schroeder (1935) Zentralblatt Mineralien: 289.

Kokkoros (1938) Prakt. Ac. Athénes: 13: 337 (Min. Abs. (1941): 8: 140).

McConnell (1940) American Mineralogist: 25: 719.

Palache, C., Berman, H., & Frondel, C. (1951), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana, Yale University 1837-1892, Volume II. John Wiley and Sons, Inc., New York, 7th edition, revised and enlarged, 1124 pp.: 756-761.

Anthony, J.W., Bideaux, R.A., Bladh, K.W., and Nichols, M.C. (2000) Handbook of Mineralogy, Volume IV. Arsenates, Phosphates, Vanadates. Mineral Data Publishing, Tucson, AZ, 680pp.: 567.

Song, Y., Zavalij, P. Y., Suzuki, M. & Whittingham, M. S. (2002): New iron(III) phosphate phases: crystal structure and electrochemical and magnetic properties. Inorganic Chemistry 41, 5778-5786.

Taxer, K. and Bartl, H. (2004): On the dimorphy between the variscite and clinovariscite group: refined finestructural relationship of strengite and clinostrengite, Fe(PO4) • 2H2O. Crystal Research and Technology 39, 1080-1088.

Internet Links for Strengite

Specimens:
The following Strengite specimens are currently listed for sale on minfind.com.

Localities for Strengite

map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.
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