Chemical elements
    History of Iron
      Native Iron
      Iron Minerals
      Sources of Iron
    Physical Properties
    Chemical Properties
    Iron Salts
    PDB 101m-1aeb
    PDB 1aed-1awd
    PDB 1awp-1beq
    PDB 1bes-1c53
    PDB 1c6o-1ci6
    PDB 1cie-1cry
    PDB 1csu-1dfx
    PDB 1dgb-1dry
    PDB 1ds1-1e08
    PDB 1e0z-1ehj
    PDB 1ehk-1f5o
    PDB 1f5p-1fnp
    PDB 1fnq-1fzi
    PDB 1g08-1gnl
    PDB 1gnt-1h43
    PDB 1h44-1hdb
    PDB 1hds-1i5u
    PDB 1i6d-1iwh
    PDB 1iwi-1jgx
    PDB 1jgy-1k2o
    PDB 1k2r-1kw6
    PDB 1kw8-1lj0
    PDB 1lj1-1m2m
    PDB 1m34-1mko
    PDB 1mkq-1mun
    PDB 1muy-1n9x
    PDB 1naz-1nx4
    PDB 1nx7-1ofe
    PDB 1off-1p3t
    PDB 1p3u-1pmb
    PDB 1po3-1qmq
    PDB 1qn0-1ra0
    PDB 1ra5-1rxg
    PDB 1ry5-1smi
    PDB 1smj-1t71
    PDB 1t85-1u8v
    PDB 1u9m-1uyu
    PDB 1uzr-1vxf
    PDB 1vxg-1wri
    PDB 1wtf-1xlq
    PDB 1xm8-1y4r
    PDB 1y4t-1ygd
    PDB 1yge-1z01
    PDB 1z02-2a9e
    PDB 2aa1-2azq
    PDB 2b0z-2boz
    PDB 2bpb-2ca3
    PDB 2ca4-2cz7
    PDB 2czs-2dyr
    PDB 2dys-2ewk
    PDB 2ewu-2fwl
    PDB 2fwt-2gl3
    PDB 2gln-2hhb
    PDB 2hhd-2ibn
    PDB 2ibz-2jb8
    PDB 2jbl-2mgh
    PDB 2mgi-2o01
    PDB 2o08-2ozy
    PDB 2p0b-2q0i
    PDB 2q0j-2r1h
    PDB 2r1k-2spm
    PDB 2spn-2vbd
    PDB 2vbp-2vzb
    PDB 2vzm-2wiv
    PDB 2wiy-2xj5
    PDB 2xj6-2ylj
    PDB 2yrs-2zon
    PDB 2zoo-3a17
    PDB 3a18-3aes
    PDB 3aet-3bnd
    PDB 3bne-3cir
    PDB 3ciu-3dax
    PDB 3dbg-3e1p
    PDB 3e1q-3eh4
    PDB 3eh5-3fll
    PDB 3fm1-3gas
    PDB 3gb4-3h57
    PDB 3h58-3hrw
    PDB 3hsn-3ir6
    PDB 3ir7-3k9y
    PDB 3k9z-3l4p
    PDB 3l61-3lxi
    PDB 3lyq-3mm8
    PDB 3mm9-3n62
    PDB 3n63-3nlo
    PDB 3nlp-3o0f
    PDB 3o0r-3p6o
    PDB 3p6p-3prq
    PDB 3prr-3sel
    PDB 3sik-3una
    PDB 3unc-4blc
    PDB 4cat-4erg
    PDB 4erm-4nse
    PDB 4pah-8cat
    PDB 8cpp-9nse

Minerals containing Iron

Copperas or melanterite, FeSO4.7H2O, occurs in nature as the result of the oxidation of pyrites or marcasite. It yields greenish, monoclinic crystals, of hardness 2, and density when pure 1.832. A rhombic variety of the heptahydrate is known as tauriscite. Heat decomposes the heptahydrates, yielding at 200° to 250° C. the monohydrate, FeSO4.H2O, found in nature as ferropalladite, and at high temperatures, ferric oxide. Copperas is isomorphous with Boothite, CuSO4.7H2O, and with pisanite, (Fe, Cu)SO4.7H2O, which latter occurs in California as blue, transparent crystals. Copperas has also been found as a bluish green crust on limonite in Carinthia. Its density is 1.8 to 1.95. The .isomorphism of these minerals is evident from the following data: -

a: b: сβ
Melanterite1.1828: 1: 1.542775° 44'
Pisanite1.1670: 1: 1.519575° 30'
Boothite1.1622: 1: 1.500074° 24'

All these minerals lose 6 molecules of water at 200° to 250° C.

Salvadorite, FeSO4.2CuSO4.21H2O, appears to be a dimorphous variety of pisanite. A ferric sulphate, Fe2(SO4)3.9H2O, occurring in hexagonal prisms in Coquimbo is known as Coquimbite. It is white to yellowish brown in colour. Janosite is a greenish yellow efflorescence occurring in Hungary, and possessed of the same composition. It crystallises in rhombic plates. The decahydrate, Fe2(SO4)3.10H2O, occurs as monoclinic crystals in quenstedtite. Ferronatrite, Na3Fe(SO4)3.3H2O, occurs as a greenish-white mineral in Chili.

Halotrichite or ferrous alum, FeSO4.Al2(SO4)3.24H2O, occurs in several localities, including Persia, where it is used by the natives for making ink. In Baluchistan it occurs as a white inflorescence on decomposed slate, and is used for dyeing, its local name being khaghal. It has recently been found in Elba in fibrous masses, white or faintly blue in colour, and possessed of a silky lustre. Density 1.90; hardness 2.5. Analysis shows a slight deficit of water due to partial dehydration in dry air.

Other sulphates are copiapite, 3Fe2O3.8SO3.27H2O; amarantite, Fe2O3.2SO3.7H2O; fibroferrite, Fe2O3.2SO3.10H2O; castanite, Fe2O3.2SO3.8H2O; botryogen, FeO.MgO.Fe2(SO4)3.18H2O; roemerite, FeSO4.Fe2(SO4)312H2O; planoferrite, Fe2O3.SO3.15H2O; paposite, 2Fe2O3.3SO3.10H2O. Iron associated with tellurium occurs as durdenite, Fe2O3.3TeO2.4H2O, in Honduras, and as emmonsite in Colorado.

Rhabdite is a crystalline phosphide of iron approximating in composition to (Ni, Fe)3P. It is found in meteorites in the form of minute tetragonal prisms. Density 6.3 to 6.8.

Vivianite, Fe3(PO4)2.8H2O, occurs as monoclinic crystals, isomorphous with erythrite, Co3(AsO4)2.8H2O, and perhaps also with annabergite, Ni3(AsO4)2.8H2O. Its crystallographic elements are: -

a: b: c = 0.7489: 1: 0.7017. β = 75° 34'.

Some specimens obtained from Cornwall are beautifully crystallised, possessing a pale, bluish green tint. Others are nodular, deep blue in colour, pulverulent, and sometimes enclose crystals of dark brown colour, which exhibit a reddish hue by reflected light. Both the green and the brown specimens yield the same results upon analysis, so that their difference in colour is most probably due to a difference in the degree of oxidation of a small portion of the iron. The crystals offer a very perfect cleavage parallel to the clino-pinacoid. The pure mineral is probably colourless, the tints usually observed being due to some of the iron becoming oxidised. The density ranges from 2.6 to 2.7. Some good crystals have yielded the value of 2.587.

The mineral was discovered by Vivian, in Cornwall, whence its name.

An earthy variety fojmd in peat mosses is known as blue iron earth.

In paravivianite, from Russia, part of the iron is replaced by manganese and magnesium, thus (Fe, Mn, Mg)3(PO4)2.8H2O. Kertschenite, (Fe, Mn, Mg)O.Fe2O3.P2O5.7H2O, likewise found in Russia, occurs as very dark green crystals.

Tamanite, the same mineral as anapaite, (Ca, Fe)3(PO4)2.4H2O, occurs in pale greenish crystalline masses.

An anhydrous mixed phosphate of manganese, calcium, and divalent iron occurs as Graftonite, (Fe, Mn, Ca)3(PO4)2, which occurs as salmon-coloured, monoclinic crystals, the crystallographic elements of which are

a: b: c = 0.886: 1: 0.582. β = 66°.

Triphyllite, Li(Fe, Mn)PO4, occurs as light green, rhombic crystals, which become dark through oxidation.

Ludlamite is a green hydrated form of ferrous phosphate found in Cornwall and elsewhere. On heating it disintegrates into bluish green plates, in contradistinction to vivianite which turns white and exfoliates under similar treatment.

Ferric phosphate occurs in nature as phospho-siderite, 4FePO4.7H2O, and strengite, FePO4.2H2O. Possibly these two minerals are the same.

A basic ferric phosphate, known as Dufrenite, Fe2(HO)3.(PO4), is found as rhombic crystals, dark green in colour, and named after Dufrenoy, the French mineralogist. Hardness 3.5 to 4; density 3.2 to 3.4. A ferric phosphate, Fe2O3.P2O5.6H2O or FePO4.3H2O, occurs in monoclinic needles as Koninckite in Belgium.

Beraunite is FePO4.2Fe2(PO4)(HO)3.4H2O, and occurs in reddish brown monoclinic crystals. Ghildrenite is a hydrated phosphate of iron and aluminium with a little manganese. It crystallises in yellow or brown rhombic prisms. When more manganese is present the mineral is called eophosphorite.

Lolingite, FeAs2, occurs in Saxony and Norway in rhombic crystals. Hardness 5 to 5.5; density 6.8 to 8.7. Greyish in colour, it gives a greyish black streak. When heated in an open tube a white sublimate of arsenious oxide or " white arsenic " is obtained; in the absence of air metallic arsenic is volatilised to a dark sublimate.

Leucopyrite, FeAs.FeAs2, resembles the previous mineral in appearance, hardness, and density.

Berthierite, FeS.Sb2S3, occurs in elongated rhombic prisms of density 4 to 4.3; hardness 2 to 3. It has a steely appearance. Heated in air, oxides of sulphur and antimony are evolved. It is readily soluble in hydrochloric acid, evolving hydrogen sulphide.

Scorodite, FeAsO4.2H2O, occurs as pale green or brown rhombic crystals of density 3.1 to 3.3; hardness 3.5 to 4. It owes its name (Greek skorodon, garlic) to the fact that, when heated, it emits the characteristic odour of arsenic. It occurs in Cornwall, and in a readily oxidisable form as a deposit from certain geysers in Yellowstone Park, U.S.A. A hydrated arsenate of iron and aluminium is known as Liskeardite.

A basic arsenate, 2FeAsO4.Fe(HO)3.5H2O, is known as iron sinter, or pharmaco-siderite in consequence of the poisonous character of arsenic (Greek pharmakon poison). It crystallises in small, green cubic crystals, for which reason it is also known as cube ore.

A hydrated arsenate of iron and calcium from Yukon is termed Yukonite. Its composition approximates to (Ca3,Fe2)As2O8.2Fe(HO)3.5H2O. It is brownish black, resinous, and amorphous. Density c. 2.65.

Ferrous antimonate, 2FeO.Sb2O5 or FeSbO3, is found in the cinnabar gravels of Tripuhy, and is termed Tripuhyte. It is dull, greenish yellow in colour, possessing a canary-yellow streak. When heated, antimony oxide vaporises, leaving ferric oxide behind. Density 5.82. Derbylite is ferrous antimonate associated with titanate, 2FeSbO3. 5FeTiO3. It crystallises in the rhombic system, its elements being

a: b: c = 0.96612: 1: 0.55025.

It is black in colour, with a resinous lustre.

An ortho-silicate of iron, termed fayalite or iron olivine, Fe2SiO4, was first found on Fayal Island in the Azores. It had crystallised in tabular rhombs of Fe2SiO4, very similar to the ferrous silicate present in certain slags. The axial ratios are

a: b: c = 0.46000: 1: 0.58112.

It is quite possible that it was simply a lump of slag from a ship's ballast. Fayalite has also been found at Rockport.

Olivine, Fe2SiO4 + xMg2SiO4, is a variable mixture of ferrous and magnesium ortho-silicates, olive green in colour, and of density about 3.3 to 3.5. It is a common constituent of rocks.

Anthophyllite, or magnesium iron metasilicate, (Mg, Fe)S2O3, crystallises in the rhombic system. A pure iron anthophyllite, FeSiO3, has been found at Rockport, but is rare. It is white to light brown in colour.

Sodium ferric metasilicate is found as acmite or aegirite, Na2Fe2(SiO3)4. Its crystals are blackish green in colour, and possess the following crystallographic elements: -

a: b: c = 1.1044: 1: 0,6043. β = 73° 27'.

Hydrated ferric metasilicates are found as Miillerite, Fe2O3.3SiO2.2H2O, and nontronite, Fe2O3.3SiO2.5H2O.

Astrolite, (Al, Fe)2Fe(Na, K)2(SiO3)5.H2O, a metasilicate of aluminium, iron, and alkali metals, occurs in Saxony as small spherical balls, with radially fibrous structure.

Glauconite, the green constituent of many rocks, if pure, would be represented by the formula KFe(SiO3)2.H2O, that is, potassium ferric metasilicate.

Cronstedtite occurs in Cornwall, associated with vivianite. It is also met with in association with Hisingerite in acicular needles in cavities in iron pyrites. Its usual structure is fibrous and radiating, and it consists essentially of ferrous silicate and hydrated ferric oxide.

Hisingerite likewise occurs in Cornwall, as dark brown, amorphous, reniform masses. Its hardness is 2.75, and density 1.74. It yields a conchoidal fracture and leaves a rust-brown streak. Its composition approximates to Fe2O3.2SiO2.2H2O.

Other silicates are pinguite, 2Fe2O3.6SiO2.3H2O + xH2O; hoeferite, 2Fe2O3.4SiO2.7H2O.

Numerous other silicates are known in which iron is one of the constituent metals. As a source of iron they are all useless for commercial purposes, since the percentage of the metal is low.

Wolframite, (Fe, Mn)WO4, is a black mineral associated with cassiterite in Cornwall and elsewhere. It yields monoclinic crystals which may be distinguished by their lustre and perfect single cleavage. Hardness 5.5; density 7.3.

Ferritungstite, Fe2O3.WO3.6H2O, an alteration product of Wolframite, is a pale ochre, which under the microscope is seen to consist of hexagonal plates.

Ferrous chloride is present inrinneite, FeCl2.3KCl.NaCl, which occurs in large, lenticular masses in beds of rock salt at Wolkramshausen in the Harz, and as a kieserite-rinneite rock in Hanover. It crystallises in the hexagonal system, and when a hot, saturated solution is allowed to cool, potassium chloride separates out.

Douglasite, FeCl2.2KCl.2H2O, occurs in the Stassfurt deposits, associated with carnallite. Density 2.16.

Ferric chloride has been found as a brown incrustation on lava, particularly in the neighbourhood of Vesuvius. It is then known as molysite, FeCl3. In combination with alkali chlorides, ferric chloride is found as kremersite, KCl.NH4Cl.FeCl3.H2O, and Erythrosiderite, 2KCl.FeCl3.H2O, both minerals being found in minute quantities in the neighbourhood of Vesuvius.

Lagonite is an ochre-coloured incrustation consisting of iron borate, Fe2O3.3B2O3.3H2O. It occurs as an incrustation by lagoons in Tuscany. A natural nitride of iron has been found in the lava of Etna, as the mineral siderazote.

For the sake of easy reference, the foregoing minerals are given in the accompanying tables, together with their chemical compositions and more important physical characteristics.

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