Rutile - Structure, crystal chemistry, and provenance

Rutile - Crystallography, Crystal Chemistry, and Provenance Potential

Rutile is one of the most common Ti minerals in the crust

It forms in some mafic igneous and metamorphic rocks.
In metamorphic rocks it is generally favored in higher P rocks
It is one of the three most refractory heavy mineral - together with zircon and tourmaline. Basis for the ZTR index.

Rutile formula and structure

Rutile is almost pure TiO2, with a tetragonal unit cell

Minor important substituent cations include

For Ti⁴⁺ we can substitute V³⁺, Cr³⁺, Al³⁺, Nb⁵⁺, Sn⁴⁺, Sb³⁺, Ta⁵⁺, W³⁺and others

Basis for Zr-in-rutile thermometer

Fig. 1 Schematic chemographic diagram of accessory phases in the system SiO2–ZrO2–TiO2. Solid solution for rutile is exaggerated for clarity. Solid solution of all phases falls within the filled circles indicating position of these phases. Note that Zr content in rutile is fixed if coexisting with quartz and zircon

The uncertainty is primarily limited by the +/- 50 C uncertainty attached to the geothermometers used to determine conditions on the calibrant samples

Basis for rutile as a provenance mineral

Fig. 2. Correlation of Zr content in rutile with peak metamorphic temperature based on an empirical calibration from 30 natural samples (Zack et al., 2004).

Fig. 4. Back scattered images of detrital rutiles from Shawangunk sample showing different degrees of alteration.

(a) Pristine detrital grain of rutile with no signs of alteration.

(b) Detrital rutile with beginning alteration. Parts of the grain are replaced by iron-rich oxides/hydroxides (white) and quartz (dark grey). Rutile still shows well-rounded grain shape and some areas of the rutile are chemically unaltered.

(c) Detrital grain with strong alteration. Whole grain is pervasively riddled with iron-rich oxides/hydroxides (white), remaining rutile is chemically enriched in Fe and surface shows dissolution features.

Fig. 6. Histogram of calculated metamorphic temperatures of metapelitic rutiles for Gloversville (UNY22), Shawangunk (UNY7) and Catskill samples (UNY13). Abundance in % of whole population. Dark grey: 63–125 um size fraction, light grey: 125–250 um size fraction. Approximate temperature regions of metamorphic facies are shown for comparison.