What is Zemannite?
Zemannite is a rare hydrated magnesium zinc iron tellurite from oxidised tellurium deposits, valued for brown lustre and a structure built around unusual tellurite groups.
Mineralogy and structure
Reference formula: Mg0.5ZnFe(III)(TeO3)3·4.5H2O. Zemannite is trigonal with the idealised formula Mg0.5ZnFe(III)(TeO3)3·4.5H2O. Hydration and cation substitutions can vary; COD 9005245 is used as a labelled representative structure. Zemannite is classified with oxides and has trigonal crystal symmetry. Typical hardness is 3–4 on the Mohs scale and specific gravity is approximately 4.3–4.5.
Colour, lustre and habit
Typical colours include brown, reddish brown, yellow-brown. The usual prismatic, tabular, granular habit and adamantine, vitreous lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Zemannite forms in or is associated with oxidised tellurium-rich hydrothermal veins and secondary cavities. Important documented localities include Moctezuma in Sonora, Mexico, and other tellurium districts.
A brown tellurite with a rare framework
Zemannite is an excellent cabinet mineral for collectors who enjoy chemistry that is hard to find in ordinary specimens. Its brown lustre becomes much more compelling alongside the tellurium-locality story.
Collecting and care
Rare and hydrated: protect from heat, water and abrasion. Tellurium-bearing material should be kept clean, enclosed and away from dust-producing work.
