Siderogel is an amorphous mineral (a mineraloid) consisting of iron(III) oxide-hydroxide FeO(OH), the same chemical compound as limonite and goethite;[1] or possibly an hydrate of the same FeO(OH)•nH
2O.[2]
Siderogel is described as blackish, brownish, or reddish-brown, often glassy and translucent.[3] It may be a gossan, the result of weathering and oxidation of sulfide ores.[4]
The International Mineralogical Association does not officially recognize siderogel as a mineral species.[5]
Siderogel has been reported in a few locations in Europe and Asia, including a site near Gavà and Bruguers, Catalunya;[1] in the mine of Codos, Aragon;[6] in the Becke-Oese quarry (now flooded) between Menden and Hemer, Germany;[3] and in the Gaosong deposit, Gejiu China.[4]