Franklinphilite
A variety of Stilpnomelane Group
What is Franklinphilite?
Franklinphilite is a phyllosilicate of the stilpnomelane group. Known from only two localities (with a third unconfirmed locality in Switzerland) It was found exclusively from the Franklin and Sterling Hill mines in Franklin, Sussex County, New Jersey. until 2013, when a locality in Wales was confirmed
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Key Characteristics
Characteristics of Franklinphilite
Franklinphilite is dark brown to black and possesses a vitreous to slightly resinous luster. It is brittle with a hardness of about 4 (Mohs) and cleaves imperfectly along the {001} plane. The density varies due to impurities, but ranges from 2.6 to 2.8 g/cm compared to the calculated value of 2.66 g/cm. It is translucent to nearly opaque, translucent in thin section and has a light brown streak. Pleochroism is distinctive with X = pale yellow and Y,Z = deep brown. Dispersion was not detected and no evident fluorescence under ultra-violet radiation was observed.
Composition of Franklinphilite
Franklinphilite has an ideal chemical formula of K4(Mn)48(Si,Al)72(O,OH)216·n(H2O) (with n~6). Reported formula is (K,Na)4(Mn2+,Mg,Zn)48(Si,Al)72(O,OH)216·6(H2O).
Quick Facts
Physical Properties
- Color
- Dark brown
- Hardness (Mohs)
- 4
Chemical Properties
- Chemical Formula
- (K,Na)4(Mn2+,Mg,Zn)48(Si,Al)72(O,OH)216 · 6H2O
- Elements
- Al, H, K, Mg, Mn, Na, O, Si, Zn
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