Akaganeite
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Akaganeite, also written as the deprecated Akaganéite, is a chloride-containing iron(III) oxide-hydroxide mineral, formed by the weathering of pyrrhotite. Wikipedia
Color: Yellowish brown, rusty brown
Crystal class: Prismatic (2/m); (same H-M symbol)
Crystal system: Monoclinic
Formula (repeating unit): Fe3+O(OH,Cl)
Space group: I2/m
Unit cell: a = 10.561, b = 3.031; c = 10.483; β = 90.63°; Z = 1