Mikrofillihartsit

Mikrofillihartsit is a micaceous silicate mineral described in some educational and regional mineralogy materials as a fine-grained, sheet-structured mineral. The name combines elements suggestive of micro-scale foliation and a mica-like habit, and it is often presented in classrooms as an example of ultra-fine phyllosilicates formed under low-grade metamorphic or hydrothermal conditions.

Composition and structure: Mikrofillihartsit is described as a phyllosilicate with layered silicate sheets built from tetrahedrally coordinated silicon and aluminum-oxygen octahedral networks. The interlayer region contains variable alkali and alkaline-earth cations and structural hydroxyl groups. No single fixed chemical formula is universally assigned; reported composition emphasizes silicon and aluminum with modest amounts of magnesium and iron, reflecting a mica-like, micrometric structure.

Physical properties: It is described as light-colored with a vitreous to pearly luster, and it is translucent to transparent in thin flakes. Mohs hardness is given in the range of 3 to 4, with perfect basal cleavage and a relatively low to moderate specific gravity (approximately 2.8–3.2). Its flaky habit and microcrystalline nature are central to its identification in thin-section observations.

Occurrence and formation: Mikrofillihartsit is said to form during late-stage alteration of feldspathic rocks via hydrothermal fluids, or in zones of microfracturing within low-grade metamorphic terrains. It commonly appears as microcrystalline aggregates intergrown with quartz, illite, and muscovite, often in fracture fills or alteration halos.

Classification and status: The term is used in some educational contexts as an example of a microcrystalline phyllosilicate, but it is not universally recognized as a formal mineral species by major authorities. Its status can vary by region or curriculum. See also phyllosilicates, mica-group minerals.