Chalcophanite



Chalcophanite is a zinc manganese oxide hydrate mineral. Some analyses were given by Palache (1935) and suggest limited Mn for Zn substitution. Criddle and Stanley (1986) reported ZnO 19.8, FeO 0.1, MnO2 65.3, H2O (by difference) 14.8, total = 100.0 wt. % for the material they studied optically. The eight analyses by Ostwald (1985) and some unpublished analyses by [Dunn] suggest that much Sterling Hill chalcophanite has near end-member composition, with very little, if any, substitution of Mg and Fe for Zn. However, banded, dull, fine-grained material in stalactitic aggregates may have much solid solution towards aurorite. Chalcophanite has been studied thermogravimetrically by Dasgupta (1974), and he also reported oriented transformations observed during heating. Although local material is Zn-dominant, much additional study and discussion of worldwide occurrences by Ostwald (1985, 1987) has led to a general acceptance of chalcophanite as a mineral name for material with widely varying composition.
Chalcophanite was first described from Sterling Hill in a superb, descriptive paper by Gideon Moore (1875); the attribution to Koenig by Frondel (1972) is in error. Roepper (1882) reported a description of a mineral he called hydrofranklinite, but this was later shown to be cospecific with chalcophanite by Penfield and Kreider (1894). X-ray data were given by Berry and Thomson (1962). Chalcophanite was verified from Franklin by [Dunn].
The crystal chemistry and the crystal structure were initially described by Wadsley (1953, 1955a). The structure was redetermined and the symmetry corrected by Post and Appleman (1988), who described it as consisting of "sheets of edge-sharing Mn4+O6 octahedra alternating with layers of Zn cations and water molecules in the stacking sequence Mn-O-Zn-H2O-Zn-O-Mn."
Chalcophanite occurs as small (<4 mm) platy crystals which are hexagonal in outline for the most part, as described by Palache (1935). Crystals also may be pseudo-octahedral or rhombic in habit. Such crystals occur as druses and also occur as foliated masses, stalactites, and plumose aggregates.
Chalcophanite also commonly occurs as crusts of radial crystals and as free-standing crystals lining vugs. Chalcophanite is dark red to black, opaque, and may have a bluish tarnish. The cleavage is perfect, appears basal on crystals of hexagonal habit, is easily developed, and is evident on even slightly altered material. The luster of freshly broken material is brilliant, splendent, and metallic; some material is dull on exposed surfaces. The density is 3.98 g/cm3. Optically, chalcophanite is uniaxial, strongly pleochroic as noted by Palache (1935), and has extremely strong anisotropism. Optical descriptions in reflected light are given by Ramdohr (1980) and Picot and Johan (1982). Full optical data are given by Criddle and Stanley (1986, 1993).
The principal occurrence of chalcophanite is at Sterling Hill, where it was found in association with goethite and manganese oxides with the hemimorphite deposits in the Passaic and Noble pits, and in the broader weathered part of the mine locally referred to as the "mud zone". Here it occurs as vuggy masses , many of which are layered, and also less commonly as druses on seams in franklinite/willemite ore. The original Sterling Hill occurrence consisted of water-worn quartz pebbles, rock fragments, and decomposed willemite, zincite, and franklinite, all held together by manganese oxides, chalcophanite among them. In general, chalcophanite is commonly associated with apparently relict franklinite, secondary goethite, hetaerolite, and hydrohetaerolite, in open-seam and porous aggregates. Birnessite, todorokite, and woodruffite are less common associated minerals.
The genesis of this occurrence has not been studied in modern times. Moore (1875) postulated that franklinite was first altered to hydrohetaerolite and limonite and that chalcophanite was formed as the result of further oxidation and hydration. This explanation was adopted by Palache who gave a description of the in situ occurrence provided by Mr. O.J. Conley (Palache, 1935, pp 22-23).
Chalcophanite occurs rarely at Franklin. It was observed associated with todorokite and hemimorphite in a vein assemblage. Some hematite associated with hemimorphite from the northern end of the Franklin Mine has been mislabeled as chalcophanite. (Dunn, 1995)


 Location Found: Franklin and Ogdensburg (Type Locality)
     
 
 Year Discovered: 1875
     
 Formula: (Zn,Fe,Mn)Mn3O7 · 3H2O
 Essential Elements: Hydrogen, Manganese, Oxygen, Zinc
 All Elements in Formula: Hydrogen, Iron, Manganese, Oxygen, Zinc
     
 IMA Status: Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
     
     
 To find out more about this mineral at minDat's website, follow this link   Chalcophanite

     
 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.586

Frondel, Clifford (1972). The minerals of Franklin and Sterling Hill, a checklist. NY.: John Willey & Sons. p.49


The Picking Table References
 PT Issue and PageDescription / Comment
View IssueV. 36, No. 2 - Fall 1995, pg. 27Closest-Packed Mineral Structures of Franklin-Ogdensburg: Kepler's Gift of the Snowflake, Part one of two parts, Paul B. Moore - Chalcophanite
View IssueV. 30, No. 1 - Spring 1989, pg. 17Research Reports, Chalcophanite
View IssueV. 14, No. 1 - February 1973, pg. 10Mineral Notes - Chalcophanite (small article)
View IssueV. 9, No. 1 - February 1968, pg. 11The Exclusive Minerals of Franklin/Ogdensburg, N.J. (as of January 1968) by Frank Z. Edwards - Chalcophanite
View IssueV. 7, No. 2 - August 1966, pg. 7The Minerals of Sterling Hill 1962-65 by Frank Z. Edwards - Chalcophanite (small article)
     
Images

     
Chalcophanite on weathered ore from the mud zone, Sterling Hill Mine, NJ.
Chalcophanite (black spherical / radial aggregates) on weathered ore from the mud zone, Sterling Hill Mine, NJ. Photo by JVF.


Chalcophanite from the Sterling Hill Mine, Ogdensburg, NJ
Chalcophanite (black to dark gray spherical aggregates) from the Sterling Hill Mine, Ogdensburg, NJ. Field of view 1". From the collection of, and photo by WP.







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