Iron(III) minerals

Hematite (), also spelled as haematite, is a common iron oxide compound with the formula Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . It has the same crystal structure as corundum () and ilmenite (). With this crystal structure geometry it forms a complete solid solution at temperatures above .

thumb|upright|Unusual specimen of goethite replacing a gypsum [[stalactite; the center is hollow. From Santa Eulalia, Chihuahua, Mexico.]] Goethite (, ) is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide, specifically the α-polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient times for its use as a pigment (brown ochre). Evidence has been found of its use in paint pigment samples taken from the caves of Lascaux in France. It was first described in 1806 based on samples found in the Hollertszu

Epidote is a calcium aluminium iron sorosilicate mineral.

Glauconite is an iron potassium phyllosilicate (mica group) mineral of characteristic green color which is very friable and has very low weathering resistance.

Aegirine is a mineral. It is a member of the clinopyroxene group of inosilicate minerals. Acmite is a fibrous green-colored variety of aegirine, with the name also used as a synonym. It was first described in 1821, in Kongsberg, Norway.

thumb|Andradite garnet – Jiangxi, Nantan, China. Andradite is a mineral species of the garnet group. It is a nesosilicate, with chemical formula Ca3Fe2Si3O12.

Jarosite is a basic hydrous sulfate of potassium and ferric iron (Fe-III) with a chemical formula of KFe3(SO4)2(OH)6. This sulfate mineral is formed in ore deposits by the oxidation of iron sulfides. Jarosite is often produced as a byproduct during the purification and refining of zinc and is also commonly associated with acid mine drainage and acid sulfate soil environments.

Lepidocrocite (γ-FeO(OH)), also called esmeraldite or hydrohematite, is an iron oxide-hydroxide mineral. Lepidocrocite has an orthorhombic crystal structure, a hardness of 5, specific gravity of 4, a submetallic luster and a yellow-brown streak. It is red to reddish brown and forms when iron-containing substances rust underwater. Lepidocrocite is commonly found in the weathering of primary iron minerals and in iron ore deposits. It can be seen as rust scale inside old steel water pipes and water tanks.

Franklinite is an oxide mineral belonging to the normal spinel subgroup's iron (Fe) series, with the formula ZnFe3+2O4.

Scorodite is a common hydrated iron arsenate mineral, with the chemical formula FeAsO4·2H2O. It is found in hydrothermal deposits and as a secondary mineral in gossans worldwide. Scorodite weathers to limonite.

Maghemite (Fe2O3, γ-Fe2O3) is a member of the family of iron oxides. It has the same formula as hematite, but the same spinel ferrite structure as magnetite () and is also ferrimagnetic. It is sometimes spelled as "maghaemite".

thumb|Garnet demantoid - Antetezambato, Ambanja District, Diana (Northern) Region, Antsiranana Province, Madagaskar. Demantoid is the green gemstone variety of the mineral andradite, a member of the garnet group of minerals. Andradite is a calcium- and iron-rich garnet. The chemical formula is Ca3Fe2(SiO4)3 with chromium substitution as the cause of the demantoid green color. Ferric iron is the cause of the yellow in the stone.

Purpurite is a manganese phosphate mineral with the formula MnPO4, with varying amounts of iron depending upon its source. It occurs in color ranges from brownish black via purple and violet to dark red.

Bixbyite is a manganese iron oxide mineral with chemical formula: . The iron/manganese ratio is quite variable and many specimens have almost no iron. It is a metallic dark black with a Mohs hardness of 6.0 – 6.5. It is a somewhat rare mineral sought after by collectors as it typically forms euhedral isometric crystals exhibiting various cubes, octahedra, and dodecahedra.

Trevorite is a rare nickel iron oxide mineral belonging to the spinel group. It has the chemical formula NiFe3+2O4. It is a black mineral with the typical spinel properties of crystallising in the cubic system, black streaked, infusible and insoluble in most acids.

Ferrimolybdite is a hydrous iron molybdate mineral with formula: Fe3+2(MoO4)3·8(H2O) or Fe3+2(MoO4)3·n(H2O). It forms coatings and radial aggregates of soft yellow needles which crystallize in the orthorhombic system.

Pharmacosiderite is a hydrated basic ferric arsenate, with the chemical formula KFe4(AsO4)3(OH)4·(6-7)H2O and a molecular weight of 873.38 g/mol. It consists of the elements arsenic, iron, hydrogen, potassium, sodium and oxygen. It has a Mohs hardness of 2 to 3, about that of a finger nail. Its specific gravity is about 2.7 to 2.9, has indistinct cleavage, and is usually transparent or translucent. It has a yellow or white streak and a yellow, green, brown or red color. Its lustre is adamantine, vitreous and resinous, and it has conchoidal, brittle and sectile fracture.

thumb|alt=text|Carminite from the Alto das Quelhas do Gestoso Mines, Gestoso, Manhouce, São Pedro do Sul Municipality, Portugal|São Pedro do Sul, Viseu District, Portugal. Picture width 8 mm thumb|alt=text|Blue scorodite crystals on red brown carminite from Alto das Quelhas do Gestoso Mines, Gestoso, Manhouce, São Pedro do Sul, Viseu District, Portugal. Picture width 3 mm. Carminite (PbFe3+2(AsO4)2(OH)2) is an anhydrous arsenate mineral containing hydroxyl. It is a rare secondary mineral that is structurally related to palermoite (Li2SrAl4(PO4)4(OH)4). Sewardite (CaFe3+2(AsO4)2(OH)2) is an ana

Magnesioferrite is a magnesium iron oxide mineral, a member of the magnetite series of spinels. Magnesioferrite crystallizes as black metallic octahedral crystals. It is named after its chemical composition of magnesium and ferric iron. The density is 4.6 - 4.7 (average = 4.65), and the diaphaniety is opaque. Occurs as well-formed fine sized crystals or massive and granular. Its hardness is 6-6.5. It has a metallic luster and a dark red streak.

Ludwigite is a magnesium-iron borate mineral: Mg2FeBO5.

Bukovskyite (also known as "clay of Kutná Hora") is an iron arsenate sulfate mineral with formula: Fe2(AsO4)(SO4)(OH)·7H2O which forms nodules with a reniform (kidney-shaped) surface. Under a microscope, these nodules appear as a collection of minute needles similar to gypsum. Some can be seen with the naked eye and occur inside the nodules.

Quenstedtite is an uncommon iron sulfate mineral with chemical formula Fe2(SO4)3·11H2O. It forms violet or white triclinic crystals. Found in oxidized zones of pyrite-rich orebodies, especially in arid climates. It was first reported in 1888 for an occurrence in Tierra Amarilla, Copiapó Province, Atacama Region, Chile and named by G. Linck in 1889 for the German mineralogist F. A. von Quenstedt (1809–1889).

Diadochite is a phospho-sulfate mineral. It is a secondary mineral formed by the weathering and hydration of other minerals. Its formula is Fe2(PO4)(SO4)OH·5H2O. Well crystallized forms are referred to as destinezite, which has been given official recognition by the International Mineralogical Association with diadochite being the poorly formed to amorphous variety.

Hisingerite is an iron(III) phyllosilicate mineral with formula . A black or dark brown, lustrous secondary mineral, it is formed by the weathering or hydrothermal alteration of other iron silicate and sulfide minerals.

Calderite is a mineral in the garnet group with the chemical formula (Mn2+, Ca)3(Fe3+, Al)2(SiO4)3.

Emmonsite, also known as durdenite, is an iron tellurite mineral with the formula: Fe2(TeO3)3·2(H2O). Emmonsite forms triclinic crystals. It is of a yellowish-green color, with a vitreous luster, and a hardness of 5 on the Moh scale. thumb|left|Emmonsite crystal spray from the Moctezuma Mine (3 mm image width) Emmonsite was first described in 1885 for an occurrence in the Tombstone District, Cochise County, Arizona. It was named for the American geologist, Samuel Franklin Emmons, (1841–1911), of the United States Geological Survey.

thumb|alt=X-ray diffraction patterns for six-line and two-line ferrihydrite.|X-ray diffraction patterns for six-line (top) and two-line (bottom) ferrihydrite. Cu Kα radiation.

Sturmanite is a rare sulfate mineral with the chemical formula Ca6Fe3+2(SO4)2.5(B(OH)4)(OH)12 · 25 H2O. It crystallises in the tetragonal system and it has a Moh's hardness of 2.5. Sturmanite has a bright yellow to amber colour and falls in the ettringite group. It was named after Bozidar Darko Sturman (born 1937), Croatian-Canadian mineralogist and Curator Emeritus of Mineralogy, Royal Ontario Museum.

Arthurite is a mineral composed of divalent copper and iron ions in combination with trivalent arsenate, phosphate and sulfate ions with hydrogen and oxygen. Initially discovered by Sir Arthur Russell in 1954 at Hingston Down Consols mine in Calstock, Cornwall, England, arthurite is formed as a resultant mineral in the oxidation region of some copper deposits by the variation of enargite or arsenopyrite. The chemical formula of Arthurite is CuFe23+(AsO4,PO4,SO4)2(O,OH)2·4H2O.

Delafossite is a copper iron oxide mineral with formula CuFeO2 or Cu1+Fe3+O2. It is a member of the delafossite mineral group, which has the general formula ABO2, a group characterized by sheets of linearly coordinated A cations stacked between edge-shared octahedral layers (BO6). Delafossite, along with other minerals of the ABO2 group, is known for its wide range of electrical properties, its conductivity varying from insulating to metallic. Delafossite is usually a secondary mineral that crystallizes in association with oxidized copper and rarely occurs as a primary mineral.

Manganvesuvianite is a rare mineral with formula . The mineral is red to nearly black in color. Discovered in South Africa and described in 2002, it was so named for the prevalence of manganese in its composition and its relation to vesuvianite.

Cyrilovite (NaFe33+(PO4)2(OH)4·2(H2O)) is a hydrous sodium iron phosphate mineral. It is isomorphous and isostructural with wardite, the sodium aluminium counterpart.

Zemannite is a very rare oxide mineral with the chemical formula Mg0.5ZnFe3+[TeO3]3·4.5H2O. It crystallizes in the hexagonal crystal system and forms small prismatic brown crystals. Because of the rarity and small crystal size, zemannite has no applications and serves as a collector's item.

Akaganeite, also written as the deprecated Akaganéite, is a chloride-containing iron(III) oxide-hydroxide mineral, formed by the weathering of pyrrhotite (Fe1−xS), an iron-deficient sulfide.

Feroxyhyte is an oxide/hydroxide of iron, δ-Fe3+O(OH). Feroxyhyte crystallizes in the hexagonal system. Feroxyhyte forms as brown, rounded to concretionary masses. Feroxyhyte is an opaque, magnetic mineral with a yellow streak and a relative density of 4.2.

Amarantite is an amaranth-red to brownish mineral with the general formula of Fe3+2O(SO4)2·7H2O or Fe3+SO4(OH)·3H2O.

Povondraite is a rare silicate mineral from the tourmaline group with formula: NaFe3+3(Fe3+4,Mg2)(BO3)3Si6O18(OH)3O. It is a dark brown to black nearly opaque mineral with a resinous to splendent luster. It crystallizes in the trigonal crystal system as equant, distorted prisms with trigonal pyramid terminations.

Schwertmannite is an iron-oxyhydroxysulfate mineral with an ideal chemical formula of or . It is an opaque tetragonal mineral typically occurring as brownish yellow encrustations. It has a Mohs hardness of 2.5 – 3.5 and a specific gravity of 3.77 – 3.99.

sorosilicates

Bonaccordite is a rare mineral discovered in 1974. Its chemical formula is Ni2FeBO5 and it is a mineral of the ludwigite group. It usually crystallizes in long, cylindrical prisms that form within another source. It is named after the area of Bon Accord, where it was first found. There have also been findings of bonaccordite within nuclear plants at multiple companies. It builds up a deposit within the machines and is a very hard mineral to clean out because it is resistant to ordinary techniques.

Bobfergusonite is a mineral with formula Na2Mn5FeAl(PO4)6. The mineral varies in color from green-brown to red-brown. It was discovered in 1986 in Manitoba, Canada, and named for Robert Bury Ferguson (19202015), a professor of geological sciences at the University of Manitoba. , the mineral has only been found in Canada and Argentina.

Slavíkite (IMA symbol: Sví) is a mineral consisting of a hydrous basic magnesium ferric sulfate with the chemical formula and is an oxidation product of pyrite in shales and slate from Bohemia. It was named in 1926 in honor of František Slavík, who was the Charles University in Prague where he was Dean of the Faculty of Science from 1924 to 1925 and Rector from 1937 to 1938.

Kankite is a mineral with the chemical formula Fe3+AsO4·3.5(H2O). Kankite is named for the locality that yielded first specimens Kaňk, Czech Republic. Kankite formation is associated with old (1200- to 1400-year-old) mine dumps. It is yellowish-green on fresh exposure, with a paler greenish yellow on exposure to air.

Esseneite is a relatively rare mineral of the pyroxene group, with formula CaFeAlSiO6. It is the ferric-iron-dominant member. Esseneite is an iron-analogue of other pyroxene-group members, davisite, grossmanite, and kushiroite. It is a metamorphic mineral forming in pyrometamorphic rocks called paralavas, which are formed due to fusing on sedimentary rocks usually in result of coal fires. Esseneite is found in both natural and anthropogenic coal-fire sites.

Zaïrite is a phosphate mineral with the chemical formula Bi(Fe3+,Al)3[(OH)6|(PO4)2]. The name was given from where it was locally discovered in Eta-Etu, Kivu, Congo (Zaïre) in 1975.

Kaatialaite (Fe(H2AsO4)3·5H2O) is a ferric arsenate mineral found in Finland.

Ikranite is a member of the eudialyte group, named after the Shubinov Institute of Crystallography of the Russian Academy of Sciences. It is a cyclosilicate mineral that shows trigonal symmetry with the space group R3m, and is often seen with a pseudo-hexagonal habit. Ikranite appears as translucent and ranges in color from yellow to a brownish yellow. This mineral ranks a 5 on Mohs scale of mineral hardness, though it is considered brittle, exhibiting conchoidal fracture when broken.

Ferri-obertiite is an amphibole group mineral that was formally approved by the International Mineralogical Association in 2015. It has the chemical formula Na(Na2)(Mg3Fe3+Ti)(Si8O22)O2.

Tripuhyite is an iron antimonate mineral with composition FeSbO4.

Coconinoite is a uranium ore that was discovered in Coconino County, Arizona. It is a phosphate mineral; or uranyl phosphate mineral along with other subclass uranium U6+ minerals like blatonite, boltwoodite, metazeunerite and rutherfordine.

Aluminocopiapite (IMA symbol: Acpi) is an aluminium iron sulfate mineral with the chemical formula AlFe(SO)(OH)·20HO. Its type localities are Fortymile River in Alaska and the San Rafael Swell in Utah. The mineral is named after the city of Copiapó in Chile.

thumb | right | Rock containing lyonsite Lyonsite (Cu3Fe+34(VO4)6) is a rare black vanadate mineral that is opaque with a metallic lustre. It crystallizes in the orthorhombic crystal system. Lyonsite often occurs as small tabular typically well formed crystals. Lyonsite has a good cleavage and a dark gray streak.

Kremersite is a rare mineral which is a hydrated multiple chloride of iron, ammonium and potassium with the formula: (NH4,K)2FeCl5·H2O. Kremersite is a brown-red to orange mineral that crystallizes in the orthorhombic system. It is a water-soluble mineral that is found around volcanic fumaroles. Occurs at Vesuvius, Italy and Mount Etna, Sicily. It was discovered in 1853 and named for the German chemist, Peter Kremers (born 1827).

Segelerite is a complex phosphate mineral with formula CaMgFe3+OH(PO4)2·H2O. It occurs in pegmatites and forms striking green or chartreuse crystals. It was discovered in 1974 in the Black Hills of South Dakota by an amateur mineralogist from New York, Curt G. Segeler (1901–1989), after whom it is named.

Tuperssuatsiaite is a rare clay mineral found in Greenland, Namibia and Brazil. It is a hydrated phyllosilicate (sheet silicate) of sodium and iron.

Alterite (IMA symbol: Atr) is a yellow-green mineral with the chemical formula ZnFe(SO)(CO)(OH)·17HO. Its type locality is Coconino County, Arizona. It is found exclusively in logs that have mineralized.

Taranakite is a hydrated alkali iron-aluminium phosphate mineral with the chemical formula .

The mineral hubeite, , is a sorosilicate of the group. Structurally it also belongs to the Akatoreite group. It was found and named after the province of Hubei, China. It is common to iron ores in a mine of that region. It occurs mainly as aggregates of fan like crystals. It is dark to pale brown, has orange-brown streak and is vitreous. Hubeite has a hardness of 5.5 in the Mohs scale, one good cleavage and conchoidal fracture. It is triclinic with a space group of P1*. The structure of hubeite is very uncommon, and in fact there is only one other mineral that fits the group, which is ruizite.

Zinclipscombite is a dark-green to brown zinc iron phosphate mineral with the formula Zn(Fe3+)2(PO4)2(OH)2. It occurs as fibrous spheres and exhibits tetragonal crystal structure.

Arakiite (IMA symbol: Ark) is a rare mineral with the formula (Zn,Mn2+)(Mn2+,Mg)12(Fe3+,Al)2(As3+O3)(As5+O4)2(OH)23. It is both arsenate and arsenite mineral, a combination that is rare in the world of minerals. Arakiite is stoichiometrically similar to hematolite. It is one of many rare minerals coming from the famous Långban manganese skarn deposit in Sweden. Other minerals bearing both arsenite and zinc include kraisslite and mcgovernite.