Nelenite is a rare manganese iron phyllosilicate arsenate mineral found in Franklin Furnace, New Jersey.

Its chemical formula is (Mn,Fe)16As3Si12O36(OH)17 or (Mn,Fe)16(Si12O30)(OH)14[As3+3O6(OH)3][2] It was first describe in 1984 for an occurrence in the Trotter Mine, Franklin Mining District, Sussex County, New Jersey.

It was named for Joseph A. Nelen of the Smithsonian Institution.

[2][4] It has also been reported from Montgomery County, Virginia and the Suceava district of Romania.

[2] At the type locality in New Jersey it occurs associated with actinolite, calcite, willemite, tirodite, rhodonite, apatite, lennilenapeite, stilpnomelane, microcline and talc.