What is a hydrous oxide of iron, occurring in prismatic crystals, also massive, with a fibrous, reniform, or stalactitic structure. The color varies from yellowish to blackish brown called?

gothite — A hydrous oxide of iron, occurring in prismatic crystals, also massive, with a fibrous, reniform, or stalactitic structure. The color varies from yellowish to blackish brown. (Webster's 1913.)

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