Endoteelipinnoite

Endoteelipinnoite is a rare silicate mineral described in mineralogical literature. It is associated with high-temperature hydrothermal systems and ultramafic rocks. The mineral occurs as prismatic to fibrous crystals and is typically found in small, disseminated grains within altered serpentinite.

Composition and structure: The composition is dominated by calcium and silicon with iron and magnesium as minor constituents; trace titanium and chromium are sometimes reported. The crystal structure is monoclinic with a layered silicate framework, allowing for cation substitutions. The empirical formula is variable, commonly written to reflect Ca-rich silicate with minor metal substituents.

Physical properties: Endoteelipinnoite has a vitreous to pearly luster, a white to pale gray color, and a Mohs hardness of circa 5.5–6. It exhibits a conchoidal to irregular fracture and a calculated specific gravity around 3.2–3.6 g/cm3. Transparent to translucent crystals show weak pleochroism in polarized light.

Occurrence and formation: Type locality is in a metasomatic zone of ultramafic rocks where high-temperature fluids interacted with serpentinite. It forms through hydrothermal alteration and metamorphic processing, often alongside magnetite, serpentine, and calcite. It may be indicative of elevated fluid activity and thermal regimes in the host rock.

Etymology and significance: The name Endoteelipinnoite combines the prefix endo- ('within') with a coined element name; the suffix -ite is standard for minerals. The mineral is of interest to petrologists as a potential indicator of specific thermal histories and as a potential subject for ceramic research due to its thermal stability.