Llisestiliite

Llisestiliite is a rare lithium-titanium silicate mineral described in the mineralogical literature as forming in high-grade metamorphic rocks and pegmatitic pockets. The idealized chemical formula is given as Li2TiSiO5, with minor substitutions such as Al for Si and Fe for Ti in natural samples. The mineral is typically found as small, euhedral crystals embedded in silicate-rich hosts.

Crystallography and structure are reported to place llisestiliite in the monoclinic system. The crystal framework comprises SiO4 tetrahedra linked to TiO6 octahedra, creating a three-dimensional silicate network that can accommodate lithium in interstitial sites. This arrangement contributes to its characteristic hardness and cleavage behavior.

Physical properties of llisestiliite include a vitreous luster, a color range from pale yellow to green, and a white streak. It is transparent to translucent in fine grains, with a Mohs hardness around 5 to 6 and a specific gravity near 3.4 to 3.7. The mineral exhibits imperfect cleavage on the {010} plane and tends to fracture conchoidally in less-coherent specimens.

Occurrence and formation are linked to metamorphic differentiation of granitoid rocks and the late-stage crystallization processes in pegmatites. Associated minerals often include quartz, garnet, cordierite, and apatite, reflecting high-temperature, low- to medium-pressure metamorphic conditions.

Etymology and naming reflect the fictional Llisse region and the customary suffix -lite used for mineral species. As a recently described, sparsely reported mineral, llisestiliite remains the subject of ongoing mineralogical study, with further analyses needed to confirm its composition, structure, and variability across localities.