Siderogel
Siderogel is an amorphous mineral consisting of iron oxide-hydroxide, the same chemical compound as limonite and goethite; or possibly an hydrate of the same •n.
Siderogel is described as blackish, brownish, or reddish-brown, often glassy and translucent. It may be a gossan, the result of weathering and oxidation of sulfide ores.
The International Mineralogical Association does not officially recognize siderogel as a mineral species.