FRANKLINPHILITE



Franklinphilite is a potassium manganese aluminum silicate hydroxide hydrate mineral of the stilpnomelane group. There is extensive solid-solution among the octahedral cations. The average of three closely agreeing microprobe analyses of the holotype yielded SiO2 44.0, Al2O3 3.6, Fe2O3 7.8, ZnO 5.9, MgO 6.4, MnO 22.3, K2O 1.5, Na2O 0.4, H2O (by difference) 8.1, total = 100 wt. %.
Franklinphilite was originally described as an unnamed Mn-dominant stilpnomelane from Franklin by Dunn et al. (1984b). Material which was more Mn-rich was subsequently described from Franklin by Dunn et al. (1992) and named franklinphilite. The crystal structure has not been determined; franklinphilite is assumed to be isostructural with ferrostilpnomelane. Franklinphilite is known only from Franklin; it has not been found at Sterling Hill.
Franklinphilite occurs in two assemblages and has a markedly different appearance in each. Material from the original assemblage (Dunn et al., 1984b) is black with vitreous luster, good cleavage, and a density of 2.75 g/cm3. Some material fitting this description is lennilenapeite; chemical analysis is needed for verification.
The holotype franklinphilite is very dark brown; the streak is light brown; and the luster is vitreous to slightly resinous. It occurs as radial clusters of platy <1 mm crystals; euhedral crystals were not observed but franklinphilite is more coarsely-crystallized at vein margins. The hardness is approximately 4, and cleavage is imperfect. The observed density is 2.6 to 2.8 g/cm3, compared with 2.66 g/cm3 (calculated). Franklinphilite is not discernibly fluorescent in ultraviolet radiation. It is best distinguished from other stilpnomelanes by chemical analysis.
The holotype franklinphilite (Dunn et al., 1992) occurs with the now-discredited baumite, first described by Frondel and Ito (1975), and discredited by Guggenheim and Bailey (1989, 1990). Franklinphilite occurred in an approximately 30-cm mass of a breccia-aggregate of calcite, willemite, aegirine, friedelite, and the lizardite-bearing, fine-grained mixture formerly known as baumite. Franklinphilite crosscuts this assemblage as a 1-cm wide vein of impure light brown material with a coarser growth of franklinphilite at the grain margins.
The other previously known assemblage (Dunn et al., 1984b) consists of black 1-3 mm franklinphilite crystals associated with nelenite, rhodonite, and tirodite. (Dunn, 1995)

 Location Found: Franklin (Type Locality)
     
 
 Year Discovered: 1992
     
 Formula: (K,Na)4(Mn,Zn,Mg,Fe)48(Si,Al)72(O,OH)216 · 6H2O
 Essential Elements: Hydrogen, Manganese, Oxygen, Potassium, Silicon
 All Elements in Formula: Aluminum, Hydrogen, Iron, Magnesium, Manganese, Oxygen, Potassium, Silicon, Sodium, Zinc
     
 IMA Status: Approved
     
     
 To find out more about this mineral at minDat's website, follow this link   Franklinphilite

     
 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.472
The Picking Table References
 PT Issue and PageDescription / Comment
View IssueV. 34, No. 1 - Spring 1993, pg. 30New-to-the-Science: Franklinphilite
     
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