Nelenite (brown) and franklinite (metallic, black), from Franklin, Franklin Mining District, Sussex County, New Jersey, US
(repeating unit)
(Mn,Fe)16As3Si12O36(OH)17 or
IMA symbolNln[1]
Strunz classification9.EE.15
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupC2/m
Unit cella = 23.24, b = 13.41
c = 7.38 [Å]; β = 105.21°; Z = 2
ColorLight to medium brown
Crystal habitCoarsely granular to massive
CleavagePerfect on {0001}
Mohs scale hardness5
LusterVitreous, resinous
StreakLight brown
Specific gravity3.46
Optical propertiesUniaxial (-)
Refractive indexnω = 1.718 nε = 1.700
Birefringenceδ = 0.018
PleochroismVisible ε = colorless and ω = light brown

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]

Discovery and occurrence

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.[4]


  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ a b c d - Nelenite
  3. ^ - Nelenite
  4. ^ a b c Handbook of Mineralogy - Nelenite