Ilmenite

oxide

rutile

Formula: Fe2+Ti4+O3
Simple oxide
Specific gravity: 4.68 to 4.76
Hardness: 5 to 6
Streak: Black to reddish brown
Colour: Black
Solubility: Slightly soluble in hydrochloric acid
Environments:

Plutonic igneous environments
Pegmatites
Carbonatites (typical)
Sedimentary environments
Placer deposits

Ilmenite is a high-temperature primary mineral that is found in igneous environments and as a constituent of black sands.
It may be found in anorthosite (R&M 93.2.146), basalt, gabbro, kimberlite and syenite. As a constituent of black sands it is associated with magnetite, rutile, zircon and monazite.

It is a mineral of the granulite facies.

Alteration

Ilmenite may alter to hematite or rutile (AJM 18.2.26).

aenigmatite, anorthite and O2 to hedenbergite, albite, ilmenite and magnetite
½Na4[Fe2+10Ti2]O4[Si12O36] + CaAl2Si2O8 + ½O2 = CaFe2+Si2O6 + 2NaAlSi3O8 + Fe2+Ti4+O3 + Fe2+Fe3+2O4
(DHZ 2A p651)

amphibole, chlorite, paragonite, ilmenite, quartz and calcite to garnet, omphacite, rutile, H2O and CO2
NaCa2(Fe2Mg3)(AlSi7)O22(OH)2 + Mg5Al(AlSi3O10)(OH)8 + 3NaAl2(Si3Al)O10(OH)2 + 4Fe2+Ti4+O3 + 9SiO2 + 4CaCO3 → 2(CaMg2Fe3)Al4(SiO4)6 + 4NaCaMgAl(Si2O6)2 + 4TiO2 + 8H2O + 4CO2
In low-grade rocks relatively rich in calcite the garnet-omphacite association may be due to reactions such as the above (DHZ 2A p453).

amphibole, clinozoisite, chlorite, albite, ilmenite and quartz to garnet, omphacite, rutile and H2O
NaCa2(Fe2Mg3)(AlSi7)O22(OH)2 + 2Ca2Al3[Si2o7][SiO4]O(OH) + Mg5Al(AlSi3O10)(OH)8 + 3NaAlSi3O8 + 4Fe2+Ti4+O3 + 3SiO2 → 2(CaMg2Fe3)Al4(SiO4)6 + 4NaCaMgAl(Si2O6)2 + 4TiO2 + 6H2O
In low-grade rocks relatively poor in calcite the garnet-omphacite association may be developed by the above reaction (DHZ 2A p453).

augite, albite, pyroxene, anorthite and ilmenite to omphacite, garnet, quartz and rutile
2MgFe2+Si2O6 + Na(AlSi3O8) + Ca2Mg2Fe2+Fe3+AlSi5O18 + 2Ca(Al2Si2O8) + 2Fe2+Ti4+O3 → NaCa2MgFe2+Al(Si2O6)3 + (Ca2Mg3Fe2+4)(Fe3+Al5)(SiO4)9 + SiO2 + 2TiO2
This reaction occurs at high temperature and pressure (DHZ 2A p449).

titanomagnetite (ilmenite combined with magnetite), quartz, and aegirine-hedenbergite to aenigmatite, hedenbergite, magnetite and O2
6(Fe2+Ti4+O3 + Fe2+Fe3+2O4) + 12SiO2 + 12(NaFe3+Si2O6 + CaFe2+Si2O6) ⇌ 3Na4[Fe2+10Ti2]O4[Si12O36] + 12CaFe2+Si2O6 + 2Fe2+Fe3+2O4 + 5O2
(DHZ p652)

Common impurities: Mn,Mg,V

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