Rutile

oxide

quartz

Formula: TiO2 simple oxide, rutile group
Specific gravity: 4.23(2)
Hardness: 6 to 6½
Streak: Greyish black
Colour: Red, blue, brown, yellow, violet
Solubility: Insoluble in hydrochloric and nitric acid; slightly soluble in sulphuric acid
Environments:

Plutonic igneous environments
Pegmatites
Carbonatites
Placer deposits
Metamorphic environments
Hydrothermal environments

Rutile is found in high pressure, high temperature igneous rocks. It is a common but not essential constituent of eclogite, and it also may be found in granite, kimberlite, mica schist and gneiss.
It often occurs as slender crystals inside quartz and mica. Rutile is found in considerable quantities in black sands associated with ilmenite, magnetite, zircon and monazite.
It is a mineral of the greenschist, amphibolite, granulite and eclogite facies.

Alteration

Hydrothermal alteration of titanium-bearing minerals commonly releases titanium, resulting in the formation of rutile or anatase. Rutile is the principle alteration mineral of ilmenite Fe2+Ti4+O3; it can replace ilmenite, and may in turn be associated with later growth crystals of ilmenite.

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.

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.

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.

Common impurities: Fe,Ta,Nb,Cr,V,Sn

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