Goethite
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Goethite is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide, specifically the α-polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient times for... Wikipedia
Category: oxide minerals hydroxide subgroup
Cleavage: Perfect
Color: Yellowish to reddish to dark brown or black
Crystal class: Dipyramidal (mmm); H–M symbol: (2/m 2/m 2/m)
Crystal system: Orthorhombic
Formula (repeating unit): α-FeO(OH)
Fracture: Uneven to splintery