ruteille

Ruteille is not a recognized mineral name. It is commonly a misspelling of rutile, a widespread titanium dioxide mineral. In scholarly and catalogued literature, the term "ruteille" does not denote a distinct species or variety; when encountered, it likely refers to rutile or to rutile inclusions within other minerals.

Rutile is TiO2 in the tetragonal crystal system. It forms prismatic crystals and slender acicular crystals known as rutile needles. The mineral typically ranges in color from brown to reddish-bold, but clear, pale, or golden varieties exist. It has a hardness of 6–6.5 on the Mohs scale and a high refractive index, giving a brilliant luster.

Rutile occurs in diverse geological settings: it forms in high-temperature metamorphic rocks such as granulites and eclogites, in igneous rocks, and in hydrothermal veins. It also occurs as inclusions in quartz and other minerals, where its needle-like crystals can be preserved.

Industrially, rutile is a principal source of synthetic titanium dioxide pigment, used to whiten and brighten paints, plastics, and paper. It is also used as a feedstock for titanium metal production and, in some contexts, as a gemstone when large, well-formed crystals are available, though such uses are rare.

The name rutile derives from Latin rutillus, meaning red; this reflects its historic association with reddish crystals. Some languages retain similar spellings that may lead to "ruteille" in non-specialist texts.