Zrinrutile

Zrinrutile is a rare oxide mineral described as a zirconium–titanium oxide with a rutile-type crystal structure. The idealized composition is (Zr,Ti)O2, with substantial substitution of zirconium for titanium and minor incorporation of niobium and tantalum. It crystallizes in the tetragonal rutile structure and typically occurs as small prismatic crystals. The mineral was first described in 2020 from high-temperature ultramafic rocks in the Osoro Complex; the name reflects its zirconium-rich composition and rutile-like topology.

Key properties include a pale yellow to brown color, adamantine to submetallic luster, and a high refractive index (approximately nω = 2.61, nε = 2.89). Mohs hardness is about 6.5, and the specific gravity ranges from 4.2 to 4.6 depending on Zr content. Cleavage is weak, and the mineral is brittle. Crystals commonly form as short prisms with a tetragonal habit; fabric is often anhedral in hand specimens.

Zrinrutile forms in high-temperature metamorphic environments and in alkaline ultramafic–igneous complexes, typically in association with rutile, ilmenite, zircon, and magnetite. It is interpreted to crystallize from Ti-rich melts or fluids under oxidizing conditions at temperatures around 800–1000°C, and it can record peak metamorphic conditions through trace-element zoning.

Significance and status: Because Zrinrutile contains appreciable zirconium, it has attracted interest as a potential trace-element carrier and geothermobarometric indicator. However, its rarity means that only a few localities are documented and comprehensive data are limited. Ongoing mineralogical work aims to confirm its stability field and establish standardized naming and classification.