Nelenite

minerals

schallerite

willemite

talc

Formula: Mn2+16As3+3Si12O36(OH)17
Phyllosilicate (sheet silicate), pyrosmalite group, paramorph of schallerite
Specific gravity: 3.46
Hardness: 5
Streak: Light brown
Colour: Light to medium brown
Common impurities: Zn,Mg,Ca,H2O
Environments

Pegmatites
Metamorphic environments

Nelenite is a rare arsenic-bearing mineral found in very few localities.

Localities

At the type locality, the Trotter mine, Franklin Mining District, Sussex county, New Jersey, USA, nelenite occurs in a metamorphosed stratiform zinc deposit in coarse-grained assemblages with pegmatitic texture. Associated minerals include actinolite, calcite, willemite, manganese-rich amphibole, rhodonite, apatite, lennilenapeite, albite, garnet, feldspar, microcline, talc and several members of the stilpnomelane group (MinMag 48.271-275, HOM). The holotype specimen is yellow willemite which is rimmed by an impure stilpnomelane-like mineral, and which is adjacent to a firm breccia that comprises most of the specimen. The breccia consists of fragments of nelenite up to 45mm across, which are in direct contact with a zinc and manganese rich actinolite, and which are surrounded by discontinuous rims of the stilpnomelane-like mineral. The cementing medium of the breccia is white calcite, and very thin films of calcite permeate the incipient cleavage of some nelenite fragments (MM 48.271-275).

At other localities there is considerable variation in the parageneses of nelenite.
In some specimens nelenite with a very low iron content is associated with zinc and manganese rich amphibole.
In others the nelenite is associated with a zinc and manganese-rich amphibole and willemite.
Another specimen has nelenite in contact with rhodonite, willemite, apatite, and lennilenapeite.
Several unanalysed specimens appear to be from a sheared amphibole-nelenite assemblage and some of the nelenite is associated with, and altered to, talc (MM 48.271-275).

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