muundurite

Muundurite is a rare phosphate mineral described as a distinct species in the early 21st century. It forms a solid solution primarily between manganese-rich and iron-rich end-members, with a framework of phosphate tetrahedra linked to octahedral sites. The idealized formula is represented as (Mn2+,Fe3+)5(PO4)3(OH)2·nH2O, acknowledging that actual compositions vary through solid solution and hydration.

Muundurite crystallizes in the hexagonal crystal system, typically forming small prismatic or tabular crystals and crusts. It has a vitreous to resinous luster, an olive-green to emerald-green color, and a hardness of 5–6 on the Mohs scale. The mineral is translucent to transparent in well-formed crystals, with no distinct cleavage and a conchoidal to uneven fracture. It is moderately dense, with a calculated specific gravity around 3.6–3.8.

Occurrence and formation: It is reported from hydrothermal veins in mafic to ultramafic rocks, often with magnetite, chlorite, and goethite as gangue minerals. Type material was described from a primary locality, with isolated reports from other regions sharing similar geological settings. Muundurite is commonly found in association with vivianite and apatite, reflecting its phosphatic nature.

Etymology and history: The name derives from the local Muundu region, honoring the geographic origin of the type material. The mineral was first described by a team of mineralogists in 2010 and has since been the subject of limited but ongoing research into phosphate solid solutions and trace-element substitution.

Uses and significance: Due to its rarity, muundurite has no commercial ore value and is primarily of interest to mineral collectors and researchers studying phosphate structures and solid-solution behavior. Safety considerations are those typical for mineral dust.