Franklinite
Franklinite is a zinc spinel, an iron zinc oxide, named for the type locality Franklin
(Sussex Co., New Jersey, USA), and for Benjamin Franklin (1706-1790) for whom
Franklin was named. With other minerals, it has been used as an ore of zinc in Franklin
and nearby Sterling Hill.
Franklinite is dark grey to black with a submetallic luster, but contrary to most
ore minerals it is not completely opaque - very thin chips are slightly translucent with
red colour. It is (was) quite abundant at Franklin and Sterling Hill, where it is often
found in a matrix of Calcite and Willemite. This material is very popular among mineral
collectors due to the vivid fluorescence in short-wave UV-light, and consequently 'dull'
rock samples may become highly cherished collectors items if they have particularly
vivid fluorescence. Contrary to popular belief, Franklinite does occur elsewhere than in
Franklin and Sterling Hill, albeit it is far more rare and does not produce as large and
rich specimens. It has been recorded as minute grains in marble in Sussex Co., New
Jersey, along a 9 mile line, and in a vein at Centerville, 5 miles from Paterson, New
Jersey. The substance has been recorded from old slag, though we will argue these are
artifacts, not minerals, older references (see Hintze, below) record it from Siegerland
(Germany) and Wyssokaja at Nijni Tagilsk (Ural, Russia), and in the 1980s it was
discovered as microscopic crystals and minute grains (to 1 mm) from Långban
(Värmlands Län, Sweden).
My records indicate that Franklinite from a range of deposits (Franklin, Sterling
Hill, and Långban) occurs on specimens that also carry one or more of the
following minerals: €girine var. Schefferite, Allactite, Andradite, Bustamite, Calcite,
Chlorophoenicite, Clinohedrite, Diopside, Erythrite, Esperite, Fluoborite, Fluorapatite,
Fowlerite, Friedelite, Glaucochroite, Hancockite, Hardystonite, Hendricksite,
Hodgkinsonite, Holdenite, Humite, Hydrozincite, Hematite, Jennite, Jerrygibbsite,
Johnbaumite, Copper, Kolicite, Kraisslite, Quartz, Lawsonbauerite, Leucophoenicite,
Löllingite, Malachite, Margarosanite, Mcgovernite, Microcline, Mooreite,
Ogdensburgite, Pharmacosiderite, Pyrobelonite, Pyrochroite, Retzian-(Nd), Rhodonite,
Rhodonite var. Fowlerite, Sarkinite, Serpierite, Sphalerite var. Cleiophane, Sussexite,
Tephroite, Willemite, Willemite var. Troostite, Yeatmanite, and Zincite.
Specimen Handling
Franklinite is for all practical purposes stable in a normal household environment. It is
not harmed by light, changes in temperature in the normal comfort range, or known to
decompose. Franklinite specimens can be fragile and should be handled with care like
any other mineral specimen. Franklinite is not appreciably soluble in water.
Bibliography
Anthony, John Williams, Richard A. Bideaux, Kenneth W. Bladh & Monte C.
Nichols. 1997. Handbook of mineralogy, vol. 3
Bancroft, Peter. 1984. Gem & Crystal Treasures.
Berthier, Pierre. 1819. Annales des Mines, 4, 489
Blackburn, William H. & William H. Dennen. 1997. Encyclopedia of mineral
names. Canadian Mineralogist, special publication 1.
Frondel, Clifford & Cornelis Klein jr. 1965. Exsolution in Franklinite.
American Mineralogist, 50(10), 1670-1680
Gaines, Richard W., H. Catherine W. Skinner, Eugene E. Foord, Brian Mason,
Abraham Rosenzweig & Vandall T. King. 1997. Dana's new mineralogy:
the system of mineralogy of James Dwight Dana and Edward Salisbury Dana, 8th
ed.
Hintze, Carl (ed.) 1921-1931. Handbuch der Mineralogie, vol. 1, section 4, part
1.
Palache, Charles. 1935. The minerals of Franklin and Sterling Hill, Sussex
County, New Jersey. Geological Survey Professional Paper, 180 [and Franklin-
Ogdensburg Mineralogical Society reprint 1974]
Palache, Charles, Harry Berman & Clifford Frondel. 1944. The system of
mineralogy of James Dwight Dana and Edward Salisbury Dana, Yale University
1837-1892, 7th ed. Vol. 1.
Ramdohr, Paul. 1980. The ore minerals and their intergrowths, 2nd ed., vols. 1-
2
Ramdohr, Paul & Hugo Strunz. 1980. Klockmann's Lehrbuch der
Mineralogie, 16th ed.
Ries, H. & W.C. Bowen. 1922. Origin of the zinc ores of Sussex Co., N.Y.
Economic Geology, 17, 517-571
Roberts, Willard Lincoln, Thomas J. Campbell & George Robert Rapp jr.
1990. Encyclopedia of Minerals 2nd ed.
Roth, H.J. 1983. Siegerland, Westerwald, Lahn und Taunus. Geologie,
Mineralogie und Paläontologie.
Shirakashi, Tadashi & Takeji Kubo. 1979. Cation distribution in Franklinite
by nuclear magnetic resonance. American Mineralogist, 64(5-6), 599-603
Sinkankas, John. 1964. Mineralogy.
This page is written and maintaned by Claus Hedegaard
