Greenish grey microcrystals of the very rare mineral minnesotaite from a locality in Michigan (Waucedah, Dickinson County, Michigan, United States of America). Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Minnesotaite
An iron-rich triclinic phyllosilicate forming fine needles and platelets — the iron analogue of talc.
Intro adapted from Wikipedia (CC BY-SA).
Minnesotaite is an IMA-recognized mineral species in the silicate class, with the chemical formula Fe²⁺₃Si₄O₁₀(OH)₂.
It crystallizes in the triclinic crystal system (space group P-1). It is a member of the Clay, Talc structural group.
Key properties: specific gravity 3.01; Greasy to waxy, dull luster; optically biaxial.
IMA symbol Mns, grandfathered status — known before the IMA’s founding, named in 1944.
Found in banded iron formations subjected to low-grade regional metamorphism.
It is found associated with Quartz, siderite, stilpnomelane, greenalite (Mesabi Range, Minnesota, USA).
The name refers to the State of Minnesota, USA, from which it was first described.