Rutile

minerals

ilmenite

zircon

monazite

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Formula: TiO₂
Simple oxide of titanium, rutile group, a tetragonal paramorph of anatase (also tetragonal) and brookite (orthorhombic)

Varieties

Ilmenorutile is a niobium-bearing variety of rutile

Crystal System: Tetragonal
Specific gravity: 4.23 measured, 4.25 calculated
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.

Localities

At Mount Moliagul, Moliagul, Central Goldfields Shire, Victoria, Australia, small groups of blood-red to brownish rutile crystals have been found in cavities in quartz (AJM 21.1.44).

At the Mount Deverell variscite deposit, Milgun Station, Western Australia, rutile occurs in the country rock and also is included in veins of variscite that have been replaced by foggite or crandallite. Also as inclusions in quartz. The variscite deposits are hosted by marine sedimentary rocks (AJM 20.2.29).

At Magnet Cove, Arkansas, USA, pseudomorphs of rutile after brookite have been found (KL p140).

The Ryerson Hill Quarry, Paris, Oxford County, Maine, USA, is in a complex pegmatite. Rutile was found in the core zone between two previously excavated pits where smoky quartz and hydroxlherderite were found. Rutile occurs as straw-colored aggregates ranging from 1 to 3 mm in size and is associated with clear to brownish gemmy microsized tourmaline rods; it is found near the contact of the pegmatite with mica schist (R&M 97.5.449).

Alteration

Hydrothermal alteration of titanium-bearing minerals commonly releases titanium, resulting in the formation of rutile or anatase (AofA). Rutile is the principle alteration mineral of ilmenite; it can replace ilmenite, and may in turn be associated with later growth crystals of ilmenite (R&M 16.2.100, AJM 18.2.26).

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).

The PT diagram below illustrates that rutile is stable at a higher temperature than anatase ( Journal of Materials Science, 46.855–874).






















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