rutielkristallen

Rutielkristallen, or rutile crystals, are crystals of the mineral rutile, a titanium dioxide (TiO2) mineral. Rutile crystallizes in the tetragonal system and commonly forms prismatic to bipyramidal crystals. The crystals are often elongated and can occur as slender needles, sometimes seen as “rutile silk” when abundant in quartz.

Rutile has a high refractive index and an adamantine to submetallic luster. Natural crystals are typically red-brown to black. On the Mohs scale, rutile hardness is about 6–6.5, and its specific gravity is around 4.2–4.3. Rutile is weakly pleochroic, with color variations along different crystal axes. It also occurs as inclusions in other minerals, most famously as slender needles in quartz.

Rutile forms as an accessory mineral in high-grade metamorphic rocks such as granulites and eclogites, and in many igneous rocks. It is widely distributed in the crust and can occur in pegmatites and placer deposits. Large, well-formed crystals exist but are relatively rare, and rutile often appears as microscopic or millimeter-scale crystals within host rocks.

Uses and significance: Rutile is a primary natural source of titanium dioxide, which is used as a white pigment in paints, plastics, and paper, as well as in ceramics and sunscreens. In geology and geochronology, rutile crystals are used for U-Pb dating to determine the ages of rocks. In petrography, rutile inclusions in quartz provide information about crystallization conditions.

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