FRANKLINFURNACEITE



Franklinfurnaceite is a calcium ferric-iron manganese zinc silicate hydroxide mineral. A microprobe analysis were given by Dunn et al. (1987b). Solid solution of non-essential elements is limited to Mg and Al; both are minor substituents. In the original description zinc was assumed to be in tetrahedral coordination, and this was validated by the solution of the crystal structure (Peacor et al., 1987b, 1988).
Franklinfurnaceite was first described from Franklin by Dunn et al. (1987b); additional X-ray data were given by Bailey (1988a), and a review was given by Bailey (1988b).
The crystal structure of franklinfurnaceite, described by Peacor et al. (1987b, 1988), is intermediate between those of chlorite and the brittle micas, having both interlayer cations and an octahedral interlayer. The structure is the first known example of: (a) a type II structure, (b) a tri-dioctahedral chlorite, and (c) a structure with calcium occupying octahedral sites between tetrahedral sheets and octahedral layers. Alternating zinc and silicon are ordered in the tetrahedral layers.
Franklinfurnaceite occurs as platy 0.3-0.5 mm crystals, tabular and composed of the pinacoid modified by a serrated, unindexed, edge form. Additional morphological description was provided by Yeates (1989). Polycrystalline aggregates are up to 1.0 cm in size. The color is invariantly dark brown, nearly black; cleavage is perfect; the luster is vitreous; the density is 3.66 g/cm3; and the mineral is extremely brittle.
There is no discernible fluorescence in ultraviolet. Franklinfurnaceite can be locally confused only with bannisterite, ganophyllite, and yeatmanite, none of which occur in the host assemblage and all of which have diagnostic properties which aid in their identification.
Franklinfurnaceite is found in unaltered, vuggy intergrowths of hodgkinsonite, clinohedrite, willemite, franklinite, and hetaerolite from the Franklin Mine. Barite and rhodonite are minor associated minerals. Although it was not noted at the time of the original description, Lawson Bauer's catalogue indicates that one of the known franklinfurnaceite specimens was found in the 436 pillar, in the 3rd slice below the 700 level, and was acquired by him from another person in 1949. A number of specimens have been found in such vuggy assemblages, and more specimens may be found by collectors and curators. (Dunn, 1995)

 Location Found: Franklin (Type Locality), unique to Franklin/Ogdensburg area
     
 
 Year Discovered: 1987
     
 Formula: Ca2Fe3+Mn32+Mn3+(Zn2Si2O10)(OH)8
 Essential Elements: Calcium, Hydrogen, Iron, Manganese, Oxygen, Silicon, Zinc
 All Elements in Formula: Calcium, Hydrogen, Iron, Manganese, Oxygen, Silicon, Zinc
     
 IMA Status: Approved
     
     
 To find out more about this mineral at minDat's website, follow this link   Franklinfurnaceite

     
 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.493
The Picking Table References
 PT Issue and PageDescription / Comment
View IssueV. 36, No. 1 - Spring 1995, pg. 11Closest-Packing and Hydrogen Bonds in Minerals of the Franklin Marble, Paul B. Moore - Franklinfurnaceite
View IssueV. 30, No, 2 - Fall 1989, pg. 7Observations of Habits for Franklinfurnaceite Crystals
View IssueV. 29, No. 2 - Fall 1988, pg. 2From the Editor's Desk, Omer S. Dean, Franklinfurnaceite - added information
View IssueV. 29, No. 2 - Fall 1988, pg. 12Mineral Notes Research Reports, Franklinfurnaceite
View IssueV. 29 No. 1 - Spring 1988, pg. 7Notes from the Laboratory & Changes to the List of Species From Franklin and Sterling Hill, Pete J. Dunn, John L. Baum, Additions to the list, Franklinfurnaceite
View IssueV. 29 No. 1 - Spring 1988, pg. 13Mineral Notes New To Science, Franklinfurnaceite
     
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