annotaatorite

Annotaatorite is a rare silicate mineral classified as an aluminosilicate. It forms in hydrothermal systems and low-grade metamorphic rocks, typically as colorless to pale yellow crystals or as microcrystalline masses. The mineral was named annotaatorite after its discovery during a rock-logging project; the name combines annotatio, Latin for annotation, with the customary mineral suffix -ite.

Chemistry and structure: Annotaatorite consists of a hydrated aluminosilicate framework that accommodates alkali and alkaline earth cations in interlayer sites. Major constituents identified by analysis are silicon, aluminum, sodium and calcium, with trace iron and titanium contributing to minor color and opacity variation. The crystal structure is layered, with sheets linked by hydrogen bonds, allowing variable interlayer occupancy that affects density and appearance.

Physical properties: It occurs as tabular to prismatic crystals up to several centimeters in length, or as fine microcrystalline masses. The color ranges from colorless to pale yellow; the streak is white. It has a vitreous luster, a Mohs hardness near 5, and a specific gravity around 3.0 to 3.4. Cleavage is imperfect in one direction; fracture is uneven. Optically, the mineral is typically transparent to translucent where crystals are well formed.

Occurrence: Type material was described from hydrothermal quartz veins in the Kestrel Gorge region. Since then, microcrystalline grains have been reported in nearby felsic volcanic rocks. Annotaatorite is primarily of academic interest, contributing to studies of silicate mineral diversity and fluid-rock interactions, with no proven industrial applications.