Lunar Mineral Found at Franklin, N.J.

By Tony Nikischer and Joe Orosz, Franklin Mineral Museum
tony@excaliburmineral.com J1OROSZ@aol.com

The mineral pyroxferroite, first described from the Sea of Tranquility on the Moon, has recently been confirmed from Franklin, Sussex Co., New Jersey. Samples of pyroxferroite were originally collected within Apollo XI mission rocks, and the mineral was described as a new species in 1970. Recent work on pyroxmangite [formula] and related species found at Franklin, New Jersey, unequivocally confirms the presence of the iron-analogue at the locality, bringing the total number of species found there to an astounding 361 as of this writing!

Ironically, the discovery of pyroxferroite at Franklin is not the first U.S. locality for the species, and it has also been confirmed from several other foreign localities as well. So while the Franklin discovery is not a unique, terrestrial occurrence, it is worthy of significant mention due to the on-going interest in Franklin mineralogy. First, however, a bit of history:

When the Fe-dominant species was first analyzed and subsequently published as a new lunar mineral in 1970, it was proposed that the well known Mn-end member pryroxmangite, and the new Fe-end-member pyroxferroite, be considered a series (the pyroxmangite-pyroxferroite series), and that the demarcation point between them would rest at the point where Fe=Mn. The lunar material was shown to be a calcian pyroxferroite, but a review of the literature pertaining to the existing Mn-end member, pyroxmangite, disclosed that five analyses of known pyroxmangite specimens, including samples from the type locality at Iva, South Carolina, were, in fact, pyroxferroite based on their Fe:Mn ratios. Hence, the “new” lunar mineral was immediately shown to exist here on earth as well, but it took the establishment of the pyroxmangite-pyroferroite series designation to uncover that fact. (There are a few other type locality minerals that have suffered this confusion, but that’s another topic for a later date!)

The discovery of this mineral at Franklin, New Jersey, is a direct result of the curiosity of the authors, the diverse and readily available reference collection at Excalibur Mineral Corp., and the subsequent analytical work performed under the auspices of the Hudson Institute of Mineralogy on the authors’ behalf.

The mineral was found at the Taylor Road Site in Franklin, Sussex Co., New Jersey, by one of the author’s (JO). The Taylor Road Site is currently owned by the Franklin Mineral Museum. It is typical of the various dump sites in the Franklin area, containing both overburden material such as dolomite, as well as ore material like franklinite with fluorescent calcite and willemite. Pyroxferroite was found here as a band of vitreous tan to yellow platy material up to 30 mm wide (specimen TS35). The assemblage in which the pyroxferroite was found is complex and quite variable in hand-sized specimens. The one characteristic mineral of this assemblage is gahnite, which appears as very dark, nearly black (green in thin section) micro crystals up to 6mm. The gahnite crystals may be disseminated or appear in bands giving hand specimens a striped appearance. The identity of gahnite was established by X-ray diffraction (XRD). Other minerals observed in the assemblage include:

Apatite (precise specie undetermined) occurs as grey masses and euhedral crystals which fluoresce orange-brown (XRD).
Calcite has been found as micro grains in thin sections (EDS).
Clinopryroxene (precise specie undetermined) is found as light to medium brown platy material (XRD).
Feldspar (precise specie undetermined) occurs as clear to white, well-cleaved masses up to several cm. that fluoresce blue.
Fluorite appears as small red-brown grains and masses (XRD).
Galena occurs as small grey metallic grains (XRD).
Garnet (likely andradite but precise specie undetermined) appears as brown grains up to 10mm
Quartz may appear as grey to white bands or micro grains in thin sections.
Pyroxmangite appears essentially identical in color and morphology to pyroxferroite.
Scheelite has been reported from this locality as white to cream fluorescent grains, but it has not been seen by the authors.
Sphalerite occurs as glassy, typically fluorescing blue-white and orange grains and masses.
Willemite has also been found as micro grains in thin sections (EDS)

Curious as to the nature of the platy, somewhat beige to yellowish mineral found in the above-described assemblage, small masses of the material were extracted from specimen # TS35 in the collection of one of the authors (JO) and subsequently powdered, and were then studied by X-Ray diffraction. The powder was examined using a Scintag XDS 2000 powder diffractometer employing a Cu K-alpha radiation source. Settings used to obtain the pattern were 45 kv and 40 ma for the X-ray source. The diffraction pattern was run through a search match routine and showed a near perfect match to ICDD file 20-0001 pyroxferroite. A good match to ICDD file 25-147 ferroan pyroxmangite was also seen. A comparision to ICDD file 29-895 synthetic pyroxmangite was relatively poor.

While the X-Ray data suggested a ferroan pyroxmangite or pyroxferroite, a chemical study was needed to precisely determine the species. First, several grains of material were extracted from specimens from the locality that were similar in appearance to TS35 described above, and a thin section from an additional sample was prepared. Utilizing a Phillips 525-M Scanning Electron Microscope (SEM) equipped with an Edax CDU super ultra thin window EDS detector and computer system, the authors found both pyroxferroite and nominal pyroxmangite in the samples. Operating conditions were set at 20 Kv throughout the analyses to maximize Mn:Fe peak responses. Typical EDS analyses of these two phases showed:

(CHART HERE)

In addition, a sample of material from Iva, South Carolina was obtained from the Excalibur inventory and analyzed as well, showing a mid-range composition in the series but clearly Fe-dominant as historically demonstrated. Samples of pyroxmangite from Japan were also analyzed and confirmed:

(CHART HERE)

Now convinced that both species could be easily separated chemically by focusing on the Fe:Mn ratio, individual grains from the powdered XRD sample from specimen # TS35 were analyzed. Four (4) grains were sampled and all showed nominal to pronounced Fe-dominance, and the average of these four analyses showed:

(CHART HERE)

Hence, while we can analytically confirm the presence of pyroxferroite in sample # TS35, our random sampling of identical appearing material showed that one or both phases could be present, and there was no visual distinction that could be made between the Mn or Fe dominant phases. While this is unsatisfying news for local collectors without a handy microprobe at their fingertips, it nonetheless properly cautions the labeling of specimens from Taylor Road as definitively one species or the other without a proper analysis.

Permission for field collecting at the Taylor Road Site has occasionally been granted by the Franklin Mineral Museum to local mineral clubs such as the Franklin Ogdensburg Mineral Society, but only on specific days and by prior arrangement. (Contact the Franklin Mineral Museum at 32 Evans Street, Franklin, New Jersey 07416, phone 973-827-3481 for further information.)

CHARTS ARE PRESENT IN THE ORIGINAL MINERAL NEWS ARTICLE ONLY

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