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Phosphosiderite from Hagendorf, municipality of Waidhaus, Upper Palatinate Forest, Bavaria, Germany

General and classification
Other names
  • Clinostrengit[1]
  • Clinostrengite[1]
  • Metastrengite[1]
  • Clinobarrandit[2]
Chemical formula Fe3+[PO4]-2H2O
Mineral class
(and division, if applicable)
Phosphates, arsenates and vanadates
System No. according to Strunz
and according to Dana
8.CD.05 (8th edition: VII/C.09)
Crystallographic data
Crystal system Monoclin
Crystal class; Symbol monoclinic-prismatic; 2/m
Room group P21/n(No 14, position 2)Template:Room group/14.2
Lattice parameters a= 5.329 to 5.330 Å; b = 9.789 to 5.809 Å; c = 8.710 to 8.714 Å
β = 90.51° to 90.60°°[3]
Form units Z = 4[3]
Twin formation Penetration twins according to {101}[3]
Physical properties
Mohs hardness 3.5 to 4
Density (g/cm3) measured: 2.74 to 2.76; calculated: 2.72 to 2.73[3]
Fissility clearly at {010}, indistinctly at {001}[3]
Fracture; Tenacity Uneven
Color reddish purple, purple, yellow orange, moss green, peach blossom red
Line colour white
Transparency transparent to translucent
Glamour Glass luster, resin luster
Crystal Optics
Refractive indices = 1.692[4]
= 1.725[4]
= 1.738[4]
Birefringence δ = 0,046[4]
Visual character biaxial negative
Axis angle 2V = 62°
Pleochroism X = light rose red, Y = carmine red, Z = colourless
Other features
Chemical behaviour very soluble in hydrochloric acid, partially soluble in nitric acid[1]

Phosphosiderite is a rather rare mineral from the mineral class of phosphates, arsenates and vanadates. It crystallizes in the monoclinic crystal system with the chemical composition Fe3+[PO4]-2H2O[3] and is thus a hydrous iron(III) phosphate.

It develops tabular crystals and penetration twins with a size of up to 2.5 cm, but also occurs in the form of fibrous, radial-rayed, racemic or kidney-shaped mineral aggregates. They are colored in various shades of red and yellow, with pleochroism occurring. The transparent to translucent crystals can be of reddish-violet (purple), peach-blossom-red, yellow-orange or moss-green colour, depending on the foreign admixture, and show a glassy to resinous luster on the surfaces.

With a Mohs hardness of 3.5 to 4, phosphosiderite belongs to the medium-hard minerals and is somewhat easier to scratch with a pocket knife than the reference mineral fluorite (Mohs hardness 4).

Etymology and history

The mineral was discovered in 1858 by Alfred Des Cloizeaux. However, he considered it to be whoreaulite. The mineral received its name phosphosiderite, which is still valid today, in 1890 from Wilhelm Bruhns and Karl Busz. The name is derived from “phospho-” for phosphorus and “-sider-” for Greek sideros (= iron).

In 1910 Alfred Lacroix discovered vilateite, which turned out to be a variety of phosphosiderite. In 1940 Duncan McConnell described clinobarrandite, which turned out to be phosphosiderite. The name metastrengite was introduced in 1951 by Clifford Frondel, Harry Berman, and Charles Palache in their 7th edition of the Dana System of Mineralogy, since phosphosiderite is an alternate modification to strengite.[4]

Only the name phosphosiderite is recognized by the International Mineralogical Association (IMA).[5]


Already in the outdated, but partly still used 8th edition of the mineral systematics according to Strunz. Edition of the mineral systematics according to Strunz the phosphosiderite belonged to the mineral class of the “phosphates, arsenates and vanadates” and there to the division of the “hydrous phosphates without foreign anions”, where it formed together with Kolbeckite, Koninckite, Malhmoodite, Mansfieldite, Metavariscite, Paraskorodite, Skorodite, Strengite, Variscite and Yanomamite the Variscite group with the system number VII/C.09 formed.

The 9th edition of Strunz’s mineral systematics, valid since 2001 and used by the IMA, also classifies phosphosiderite in the division of “Phosphates etc. without additional anions; with H2O”. However, this is further subdivided according to the size of the cations and the amount of the water of crystallization, so that the mineral is to be found according to its composition in the subdivision “With exclusively medium-sized cations; RO4 : H2O = 1 : 2”, where it is with kolbeckite and metavariscite in the metavariscite group with the system number 8. CD.05.

The system of minerals according to Dana, which is predominantly used in English-speaking countries, also classifies phosphosiderite in the class of “phosphates, arsenates and vanadates” and there in the division “hydrous phosphates etc.” (No. 40) and there in the subgroup “hydrous phosphates etc., with A3+XO4 × x(H2O)” (No. 40) and there into the subgroup “Hydrous phosphates etc., withA3+XO4× x(H2O)”. Here it can also be found together with kolbeckite and metavariscite in the metavariscite group with the system number 40.04.03.

Crystal structure

Phosphosiderite crystallizes isotypically to metavariscite[6] monoclinic in space group P21/n(space group no. 14, position 2)Template:Space group/14.2 with lattice parameters a= 5.329 Å, b = 9.789 Å, c = 8.710 Å and ß = 90.60° and four formula units per unit cell.[3]

The phosphate group ([PO4]3-) forms tetrahedral units of quadruply coordinated phosphorus atoms. The iron atoms are also fourfold coordinated. Bonds exist only between iron and oxygen and phosphorus and oxygen. In theory, both the iron and the phosphorus atoms should be in the +4 oxidation state, but the real electron distribution is such that phosphorus is five times positive, and iron only three times. The crystal water molecules are located in a larger cavity, which is formed once per elementary cell and is surrounded by iron, phosphorus and oxygen.[1]

Modifications and varieties

The compound Fe3+[PO4]-2H2O is dimorphic and occurs in nature as orthorhombic crystallizing strengite in addition to the monoclinic crystallizing phosphosiderite.[6]

Vilatite is the name given to a manganese-rich variety of phosphosiderite.[7][8]

Formation and sites

Phosphosiderite forms as a secondary mineral to triphyline in pegmatite rocks. It is associated with triphyline, barbosalite, leucophosphite, laueite, hureaulite, strengite and turquoise.[3]

As a rather rarely occurring mineral formation, phosphosiderite can be partly abundant at various localities, but overall it is not very common. About 200 localities are known so far (as of 2015).[9]

The type locality (site of first description) of phosphosiderite is in Germany at the Kalterborn Mine, Eiserfeld, Siegerland, North Rhine-Westphalia. Other localities in Germany are in Oberwolfach in the Black Forest (Baden-Württemberg). In Bavaria there are some more localities. In Lower Bavaria there is a locality in Rabenstein (municipality Zwiesel), in the Upper Palatinate some in Auerbach, Pleystein, Plößberg, Waidhaus and Waldmünchen. In Hessen there is only one place of discovery, this is in Essershausen, market town Weilmünster, district Limburg-Weilburg. In North Rhine-Westphalia there are besides the type locality two localities in the Sauerland (in Arnsberg and Meschede), furthermore there is another locality near the type locality in Eiserfeld(Eisenzecher Zug Mine). Another German locality is in Schleswig-Holstein in Joldelund, district Nordfriesland.[10]

In Austria there is one known locality. It is located in Styria in Herzogberg (municipality Kindberg) in the mountain range Koralpe.[10]

In Switzerland, there is one locality in the canton of Ticino in Brissago.[10]

Other localities include Argentina, Australia, Belgium, Brazil, Cameroon, Canada, China, Colombia, Finland, France, Ireland, Italy, Japan, Libya, Madagascar, Morocco, Portugal, Russia, Rwanda, Spain, South Africa, Sweden, the Czech Republic Hungary, the United Kingdom and the US states of Alabama, Arizona, Arkansas, California, Colorado, Florida, Georgia, Indiana, Maine, Maryland, Nevada, New Hampshire, New Jersey, North Carolina, South Dakota, Utah, Virginia and Wisconsin.[10]

Use as a gemstone

Phosphosiderite is of little importance as a gemstone for commercial use, as its low Mohs hardness of 3.5 to 4 actually makes it too soft and would scratch quickly. In the form of tumbled stones, cabochons or spherical beads, however, it is occasionally processed into various pieces of jewelry.[11]

See also

  • List of minerals


  • Willy Bruhns, Karl Busz: Phosphosiderit, ein neues Mineral von der Grube Kalterborn bei Eiserfeld im Siegenschen. In: Journal of Crystallography and Mineralogy. Vol. 17, 1890, pp. 555-560.
  • Phosphosiderites. In: Clifford Frondel, Harry Berman, Charles Palache (eds.): Dana’s System of Mineralogy. 7. Edition. 1951, pp. 796-771 ( [ PDF]).
  • Duncan McConnell: Clinenobarrandite and the isodimorphous series, variscite-metavariscite. In: American Mineralogist. Vol. 25, 1940, pp. 719-725 ( [PDF]).

Web links

Commons: Phosphosiderites– Collection of images, videos and audio files

Individual references

  1. a b c d e
    Mineral Atlas:Phosphosiderite

  2. Mindat – Clinobarrandite
  3. a b c d e f g
    Phosphosiderites. In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (eds.): Handbook of Mineralogy. Mineralogical Society of America, 2001( [PDF]).
  4. a b c d e
    Mindat – Phosphosiderites

  5. Commission on new minerals and mineral names. In: Mineralogical Magazine. Volume 36. International Mineralogical Association, 1967, p. 135 ( [PDF]).
  6. a b
    Paul B. Moore: The crystal structure of metastrengite and it’s relationship to strengite and phosphophyllite. In: American Mineralogist. Volume 51. Mineralogical Society of America, 1966 ( [ PDF]).

  7. Friedrich Klockmann: Klockmanns Lehrbuch der Mineralogie. Ed.: Paul Ramdohr, Hugo Strunz. 16. Edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8, p. 640 (first edition: 1891).

  8. Mindat – Vilateite

  9. Mindat – Number of localities for phosphosiderite
  10. a b c d
    List of locality for phosphosiderite at Mineralienatlas and at Mindat

  11. – Phosphosiderite with picture examples of cut stones