rutile

Rutile is a mineral composed of titanium dioxide (TiO2). It is the most common natural form of TiO2 and the stable tetragonal polymorph at most conditions. Rutile is a widespread accessory mineral in igneous and metamorphic rocks and also occurs as detrital grains in sedimentary rocks and heavy mineral sands. Its crystal system is tetragonal and it often forms elongated, needle-like or prismatic crystals.

Physical properties include a Mohs hardness of 6–6.5 and a specific gravity of about 4.2–4.3. Color ranges from reddish-brown through yellow-brown to black, with a luster described as adamantine to submetallic. Rutile is transparent to opaque and shows birefringence under polarized light. The common habit is prismatic and acicular, and rutile crystals frequently occur as inclusions in other minerals such as quartz, corundum, and zircon.

Geologically, rutile forms in high-temperature environments and is commonly associated with minerals like ilmenite, magnetite, and zircon. It occurs in both igneous and metamorphic rocks and is a major constituent of heavy mineral sands as detrital grains resulting from weathering and erosion of older rocks.

Uses are primarily as a source of titanium. Titanium metal is produced from TiO2 by reduction processes such as the Kroll method, while TiO2 is also mined as a pigment for paints, coatings, plastics, paper and sunscreen, valued for its high refractive index and brightness. Rutile-rich concentrates are mined for both metal production and pigment manufacture.

Name-wise, rutile derives from Latin rutilus, meaning red or golden-red, reflecting the common reddish-brown color of many specimens.