Images
Formula: Mn2+16As3+3Si12O36(OH)17
Phyllosilicate (sheet silicate), pyrosmalite group,
paramorph of
schallerite,
manganese-bearing mineral
Crystal System: Trigonal
Specific gravity: 3.46 measured, 3.45 calculated
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).
Back to Minerals