Rutile is a common accessory mineral in high-temperature and high-pressuremetamorphic rocks and in igneous rocks.
Thermodynamically, rutile is the most stable polymorph of TiO2 at all temperatures, exhibiting lower total free energy than metastable phases of anatase or brookite.[5]Consequently, the transformation of the metastable TiO2 polymorphs to rutile is irreversible. As it has the lowest molecular volume of the three main polymorphs; it is generally the primary titanium bearing phase in most high-pressure metamorphic rocks, chiefly eclogites.
Rutile in quartz
Within the igneous environment, rutile is a common accessory mineral in plutonicigneous rocks, though it is also found occasionally in extrusive igneous rocks, particularly those that have deep mantle sources such as kimberlites and lamproites. Anatase and brookite are found in the igneous environment particularly as products of autogenic alteration during the cooling of plutonic rocks; anatase is also found inplacer deposits sourced from primary rutile.
The occurrence of large specimen crystals is most common in pegmatites, skarns, andgranite greisens. Rutile is found as an accessory mineral in some altered igneous rocks, and in certain gneisses and schists. In groups of acicular crystals it is frequently seen penetrating quartz as in the flches d'amour from Graubnden,Switzerland. In 2005 the Republic of Sierra Leone in West Africa had a production capacity of 23% of the world's annual rutile supply, which rose to approximately 30% in 2008. The reserves, lasting for about 19 years, are estimated at 259,000,000 metric tons (285,000,000 short tons).[6]
