Nelenite



Nelenite is a manganese iron arsenic silicate hydroxide mineral of the friedelite group. In contrast to schallerite, Fe substitutes for Mn to a large extent and comprises up to 5.8 of the 16 octahedrally coordinated cations. In addition, Zn, Mg, and Ca also substitute for Mn, in small yet consistent amounts. Because Fe3+ may play a role in other manganese arsenic silicates, the oxidation state of Fe in nelenite was carefully checked and found to be almost wholly divalent.
Nelenite was originally described as ferroschallerite by Bauer and Berman (1930). The name was in allusion to the chemical similarity to schallerite and the presence of much Fe in the material. This mineral was later re-examined by Frondel and Bauer (1953) who, on the basis of its X-ray powder diffraction pattern, discredited it as an As-bearing type of friedelite; Hey (1956) suggested that this discreditation of ferroschallerite as friedelite was premature. Subsequent to the re-characterization of schallerite by Dunn et al. (1981c), ferroschallerite was re-examined and found to be a polymorph of schallerite (Dunn and Peacor, 1984). Because this phase does not have the schallerite structure and has Mn > Fe in all specimens the older name was discarded as a gross misnomer, and the mineral was renamed nelenite. Nelenite is isostructural with friedelite and/or mcGillite. It was found only at Franklin.
Nelenite is found as anhedral fragments up to 30 x 45 mm in size, with perfect cleavage; no euhedral crystals have been found. It is distinctly brown; turbid material is light brown. The luster is vitreous. The density is 3.46 g/cm3 (meas.), 3.45 g/cm3 (calc.). Nelenite is not discernibly fluorescent in ultraviolet. Broken fragments resemble some local manganoan diopside (schefferite) or yeatmanite. Nelenite is easily distinguished from these two minerals by its optical character and lower indices of refraction, respectively. Nelenite is distinguished from friedelite by higher indices of refraction and from schallerite by its X-ray powder pattern and perfect cleavage.
Nelenite was first found in 1925 and reportedly came from the 1597 pillar, approximately 50 feet south of the Trotter Shaft at Franklin. The type material is associated with light-yellow willemite which is rimmed by a stilpnomelane-group mineral. The type specimen is a breccia consisting of actinolite, calcite, nelenite, and willemite. Although Bauer and Berman (1930) referred to this amphibole as zinc-manganese-cummingtonite (later shown to be tirodite), their reference was to other nelenite samples.
The known nelenite specimens apparently came from at least four assemblages, as evidenced by textural relations and the compositions of the associated amphiboles (Dunn and Peacor, 1984). Four specimens are found with zincian, ferroan tirodite and spessartine; two of these four are also associated with franklinphilite. In addition, a complex sample has nelenite associated with willemite, rhodonite, apatite, and lennilenapeite (Dunn et al., 1984b). (Dunn, 1995)


 Location Found: Franklin (Type Locality)
     
 
 Year Discovered: 1984
     
 Formula: (Mn,Fe)16(Si12O30)(OH)14[As33+O6(OH)3]
 Essential Elements: Arsenic, Hydrogen, Manganese, Oxygen, Silicon
 All Elements in Formula: Arsenic, Hydrogen, Iron, Manganese, Oxygen, Silicon
     
 IMA Status: Approved
     
     
 To find out more about this mineral at minDat's website, follow this link   Nelenite

     
 References:
Dunn, Pete J. (1995). Franklin and Sterling Hill New Jersey: the world's most magnificent mineral deposits. Franklin, NJ.: The Franklin-Ogdensburg Mineralogical Society. p.480


The Picking Table References
 PT Issue and PageDescription / Comment
View IssueV. 25 No. 2 - Fall 1984, pg. 7Mineral Notes New To Science, Nelenite
View IssueV. 24, No. 1 - Spring 1983, pg. 12Mineral Notes A Mineral New To Science, Nelenite
     
Images

     
Nelenite, calcite and franklinite from Franklin, NJ
Nelenite (light brown), calcite (white) and franklinite (black) from Franklin, NJ. From the collection of, and photo by Robert A. Boymistruk.







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