ALLANITE-(Ce)


{CaCe}{Al2Fe2+}(Si2O7)(SiO4)O(OH),
calcium cerium aluminum iron silicate oxyhydroxide




Nomenclatural note:  The most common allanite species in the Franklin area, as suggested by the title above, is allanite-(Ce), the cerium-dominant member of the allanite group.  Despite their widespread nature, the local allanite-group minerals have not been analyzed from all known assemblages, and the rare-earth dominance for some of them remains undefined.  For that reason we refer simply to “allanite” below, with no elemental suffix denoting a specific species.

Allanite, a rare-earth-bearing group of minerals belonging to the epidote supergroup, is a common accessory component of the late- to post-orogenic intrusive rocks of the New Jersey Highlands, including the microcline-quartz pegmatites of the Franklin area.  It was first reported by Jackson (1850) in pegmatitic rocks on the dumps of one of the local iron mines.  Within the Franklin orebody it has been found in other rock types as well (notably in the minehillite assemblage; Dunn et al., 1984), but it has not yet been reported from Sterling Hill.  Allanite almost invariably forms black, tabular to bladed crystals, most 1-2 cm in length, but crystals as long as 15 cm are known.  Some are quite well-formed (ALL6), though Palache (1935, p. 98) remarked on their commonly dull luster.  Large crystals are rarely recovered intact due to the extreme brittleness of the mineral, as remarked upon by several authors.

The majority of allanites worldwide are at least somewhat radioactive due to thorium substituting for Ca and Ce.  Alpha particles emitted by the thorium gradually destroy the allanite crystal structure, ultimately converting it to an amorphous (metamict), glasslike material that, for many minerals, is much more susceptible to alteration and hydration than the original mineral.  In the Franklin area, radiation-induced damage and concomitant expansion of allanite mineral grains are commonly expressed in a series of small fractures radiating into the surrounding mineral grains, as shown in photo ALL7 below. Similar fracture haloes around allanite grains were observed in numerous other specimens.  In addition, iron leached from altered allanite grains is commonly reprecipitated as brown to red, limonitic to hematitic haloes around the grains (ALL5b, ALL7) and renders them readily visible in the field.

Tabular allanite crystals as much as 7.5 cm long and nearly 4 cm wide have long been known from the Franklin area, especially from the Trotter mine (Eakle, 1894), but most are much smaller, rarely exceeding 2 cm in length.  An exceptionally large allanite crystal is shown here as specimen ALL8 from a locality north of Andover.  Allanite is of widespread occurrence and may still be found on the Buckwheat dump, the Trotter dump, in the Double Rock pegmatite just north of the Buckwheat pit, the Hamburg quarry (ALL7), and in numerous other areas where feldspathic pegmatitic rocks are exposed.  More interesting in some ways are allanite specimens from the Franklin orebody (e.g., allanite in rhodonite; ALL9), but these are available only from old collections.

References

Betancourt, P.P. (1989), The epidote-pyroxene-fluorapophyllite assemblage in the Franklin mine at Franklin, New Jersey.  The Picking Table, vol. 30, no. 1, p. 8-10.  [Mentions allanite crystals with brown alteration haloes in epidote-pyroxene veins cutting the local gneisses, pegmatites, and ore]

Dunn, P.J. (1995), Franklin and Sterling Hill, New Jersey:  the world’s most magnificent mineral deposits.  Privately published in five volumes, 755 pp.  [Reconfirms the Ce-dominant nature of Franklin allanite and provides brief descriptions of the two major assemblages for allanite in the Franklin area]

Dunn, P.J. and Baum, J.L. (1988), Notes from the laboratory and changes to the list of species from Franklin and Sterling Hill.  The Picking Table, vol. 29, no. 2, p. 3.  [Mentions that Franklin allanite is cerium-dominant, so should be referred to as allanite-(Ce) instead of just allanite]

Eakle, A.S. (1894), On allanite crystals from Franklin, N.J.  American Journal of Science, 3rd series, vol. 47, no. 282, p. 436-439.  [Studied numerous crystals of allanite from the Trotter mine; lists 14 crystal forms present and provides crystal drawings.  Also provides optical data]

Eakle, A.S. (1894), XII. Über Allanit und Tourmalin aus New Jersey.  Zeitschrift für Krystallographie und Mineralogie, vol. 23, no. 106, p. 209-211.

Frondel, Clifford (1972), The minerals of Franklin and Sterling Hill - a check list.  Wiley-Interscience, 94 pp.  [Describes allanite as “not rare” in the pegmatites of the Balls Hill magnetite deposits and in the Trotter mine; see p. 40]

Frondel, J.W. (1964), Variation of some rare earths in allanite. American Mineralogist, vol. 49, nos. 9 and 10, p. 1159-1177.  [A study of allanite from 51 worldwide localities, including Franklin.  Analysis of the rare-earth contents of these allanite samples shows for nearly all of them, the Franklin sample included, that Ce is the dominant rare-earth element]

Hunt, T.S. (1861), Allanite.  Boston Society of Natural History Proceedings, vol. 8, p. 57.  [Provides a chemical analysis of the allanite reported by Jackson (1850); analysis reprinted in Palache (1935), p. 99]

Jackson, C.T. (1850), Description and analysis of allanite from Franklin, New Jersey.  American Association for the Advancement of Science Proceedings, vol. 3, p. 323-324 (published in 1851). [First identification of allanite from the dump of one of the iron mines in the Franklin area]

King, V.T., King, N.E., Betancourt, P.P., Bostwick, R.C., Chin, Peter, Hecht, T.J., Kuitems, S.M., Moritz, Harold, Nemetz, J.D., Nikischer, A.J., Sanford, Stephen, Van Fleet, J.A., and Verbeek, E.R. (2021), The Mineralogy of Franklin and Ogdensburg, New Jersey—A Photographic Celebration. Privately published, 1400 pp. [Photographs of allanite-(Ce) on p. 603-604, 621, and 763-765]

Palache, Charles (1935), The minerals of Franklin and Sterling Hill, Sussex County, New Jersey.  U.S. Geological Survey Professional Paper 180, 135 pp.  [Describes allanite on p. 98-99; provides a list of the crystal forms observed, reprints Hunt’s earlier (1861) chemical analysis, and shows on Plate 16 a photograph of a splendid allanite crystal in pegmatite]



Images




Black, tabular 4-7 mm long grains of allanite embedded in coarse-grained feldspar
Earl R. Verbeek
The black, tabular grains of allanite in this specimen are 4-7 mm long and lie embedded in coarse-grained feldspar, probably microcline. This is the typical form of allanite from Franklin; numerous examples exist. The allanite grains upon close inspection show a well-developed pattern of radial cracks indicative of lattice expansion upon metamictization.  The green mineral is epidote, a hydrothermal alteration product of the feldspar. Steven Phillips collection; formerly in the Lee Areson (LA966) and Gary Grenier (GG 797) collections.

Identifier: ALL2a
Locality: Franklin (area)
Specimen size: 10 x 6 x 1 cm





Black, tabular 1-2 cm long grains of allanite embedded in coarse-grained feldspar with minor quartz.
Earl R. Verbeek
This specimen is similar to ALL2a but differs from it in the larger size of its allanite crystals, which here are 1-2 cm long. The crystal exposed along the far right edge of the specimen shows well the thin-bladed habit of the allanite. The matrix is coarse-grained feldspar with minor quartz. This specimen was collected by Gary Grenier in October 1970 and was specimen GG 392 in his collection; it is presently (2017) in the collection of Steven Phillips.

Identifier: ALL1a
Locality: Franklin (area)
Specimen size: Not measured; estimated 10 cm across





Glassy, nearly black allanite, most 4-7 mm in length on ivory-colored feldspar partly altered to green epidote
Earl R. Verbeek
Numerous crystals of glassy, nearly black allanite, most 4-7 mm in length, are shown here in a matrix of medium-grained, ivory-colored feldspar partly altered to green epidote. The orange stains around the allanite grains formed as iron, leached from the allanite during alteration, was reprecipitated locally as limonite. Also present in this specimen are tiny but well-formed, clove-brown grains of zircon. A few scattered grains of calcite, white and inconspicuous in daylight but showing bright orange-red fluorescence SW, suggest derivation of this specimen from in or near the Franklin orebody. The black rim at upper right is part of the weathering rind of the original rock. This specimen was collected in the late 1980s by Ron DeBlois and remains in his collection.

Identifier: ALL5a
Locality: Site of Mill no. 2 (“Palmer mill”), Franklin
Specimen size: 15 x 11 x 6 cm



Glassy, nearly black allanite, most 4-7 mm in length on ivory-colored feldspar partly altered to green epidote
Earl R. Verbeek
Close-up view of bladed allanite crystals in the specimen ALL5a.

Field of view: The horizontal width is 6.8 cm.

Identifier: ALL5b
Locality: Site of Mill no. 2 (“Palmer mill”), Franklin
Specimen size: 15 x 11 x 6 cm





Sharply formed, bladed allanite crystal, 4 cm long, matrix of medium-grained, bluish-green microcline and quartz
Earl R. Verbeek
A sharply formed, bladed allanite crystal, 4 cm long, 2.7 cm wide, and 0.7 cm thick, in a matrix of medium-grained, bluish-green microcline and quartz (both somewhat iron-stained on front surface as photographed). The top of the crystal is not broken; it is a planer crystal face with a little embedded milky quartz. This is an uncommonly large allanite crystal, and as good as they get. National Museum of Natural History specimen C312 x.

Identifier: ALL6b
Locality: Franklin (area)
Specimen size: 7 x 6 x 4 cm





Black allanite crystal 1 cm long, embedded in microcline-quartz pegmatite
Earl R. Verbeek
A black allanite crystal 1 cm long, embedded in a freshly blasted mass of microcline-quartz pegmatite from a local quarry a few kilometers north of Franklin. A network of small fractures radiating outward from the allanite grain, indicative of radiation damage and consequent lattice expansion of the allanite, is well shown in this view.

Identifier: ALL7a
Locality: Hamburg quarry, Hamburg, NJ
Specimen size: ca. 1 cm crystal





Large allanite crystal, slightly more than 15 cm long, embedded in microcline-quartz pegmatite rock
Earl R. Verbeek
An uncommonly large allanite crystal, slightly more than 15 cm long, embedded in microcline-quartz pegmatite rock from a locality about 14 km southwest of Franklin. This crystal was found in 2005 by Earl Verbeek in a boulder of recently blasted rock from a site being cleared for a housing development adjacent to County Route 517 near Perona Farms. The rubble from that operation has since been removed or covered.

Identifier: ALL8a
Locality: South side of County Route 517 (Andover-Sparta Road), about 0.5 km southwest of Perona Farms, Andover Township, New Jersey.
Specimen size: 15 cm crystal





Allanite crystals in pegmatite matrix rock
Earl R. Verbeek
Abundant allanite crystals in pegmatite matrix rock from an undisclosed locality in the Franklin area. This specimen at one time had been mislabeled and sold as warwickite, which it somewhat resembles, but the matrix is feldspar rather than Franklin Marble. It later became part of the sales stock of the Franklin Mineral Museum.

Identifier: ALL12a
Locality: Franklin (area)
Specimen size: 17 x 10.5 x 2.5 cm





Black, bladed crystals of allanite in a coarse-grained matrix of pink rhodonite, bone-white calcite
Earl R. Verbeek
Black, bladed crystals of allanite, several of them 1-2 cm long but numerous others much smaller, in a coarse-grained matrix of pink rhodonite, bone-white calcite (fl. bright orange-red SW), and a little secondary willemite. This is a rare matrix for local allanite, most of which formed as a minor constituent of the local post-orogenic pegmatites, but here it is present in a calcium-silicate matrix rock from within the Franklin orebody. The allanite in this specimen, now no. FMM-7999 of the Franklin Mineral Museum, was confirmed by Raman spectroscopy. It was purchased from Mark Leger in 2018 and previously was specimen F601CL in the collection of Chet Lemanski.

Identifier: ALL9a
Locality: Franklin mine, Franklin
Specimen size: 12.5 x 7.5 x 6 cm