Loellingite is an iron arsenide mineral of the loellingite group. Few analyses have been made of local material. Radcliffe and Berry (1968; unpublished data on file at the Smithsonian Institution) found Franklin loellingite to contain 99.8 mole % FeAs,. [Dunn's] unpublished analyses of several loellingites found them to have near end-member composition.
Loellingite is the most common arsenide at both deposits; the other common arsenic-bearing mineral is arsenopyrite. In general, loellingite is found within the orebodies, whereas arsenopyrite is found predominantly in the marble.
Loellingite was first reported from Franklin by Brush (1871) and subsequently by Bauer and Berman (1927); the results of the latter study were summarized by Palache (1935).
The crystal structure was described by Buerger (1932) and the unit-cell was refined by Peacock (1941, 1944), who also provided X-ray powder data; both obtained data from the material of Bauer and Berman. Davis (1985) provided descriptions of the occurrence in the black-willemite zone at Sterling Hill.
Loellingite occurs in euhedral crystals; those seen by the writer resemble the habits illustrated by Bauer and Berman (1927) and Palache (1935). Most crystals are slightly tabular and prismatic to dipyramidal in habit; many have rounded coigns. It also occurs as masses, interstitial fillings, and granules in high-temperature assemblages. The color is brilliant silver-white; the luster is metallic; and it is opaque and brittle. The density is 7.53 g/cm3 (Buerger, 1932), 7.43 g/cm3 (Peacock, 1941). It is easily confused with arsenopyrite, although arsenopyrite is commonly prismatic in habit; mineral associations are helpful in distinguishing them, inasmuch as arsenopyrite is only rarely found in the orebodies. Although only a general rule-of-thumb, Franklin loellingite crystals are commonly euhedral and have bright luster, whereas those at Sterling Hill are more rounded, distorted, and have duller luster.
In general, loellingite is found within the orebodies and is commonly associated with calcite or sphalerite in addition to other species. It is moderately common in small amounts, but is not generally abundant.
At Franklin, the first report was of an association with cubic gahnite by Brush (1871). The crystals described by Bauer and Berman (1927) from the 750 level were associated with pyroxene, calcite, and franklinite. Bauer and Berman also reported an occurrence with gahnite at the Trotter Shaft. Studies by [Dunn] have found loellingite associated with almandine, magnetite, and fayalite. A significant Franklin occurrence is of nickeloan material associated with gersdorffite, rammelsbergite, and nickeline from the Trotter Mine. In this assemblage, described herein under nickeline and in great detail by Oen et al. (1984), loellingite is among the last arsenides to form.
At Sterling Hill, loellingite is found in a number of diverse assemblages, most commonly associated with sphalerite. It is also found with bornite and magnetite slightly above the 1300 level; with calcite on the 340, 1000, 1100, 1200, 1500, and 1600 levels; and variously associated with sphalerite, fluorite, pyroxene, magnetite, franklinite, and calcite in numerous places in the mine. The most significant Sterling Hill occurrence is one in which it is associated with black willemite, fayalite, and calcite; this material has provided fine crystals. Loellingite may be a source of As for secondary arsenate minerals. (Dunn, 1995)

 Location Found: Franklin and Ogdensburg
 Formula: FeAs2
 Essential Elements: Arsenic, Iron
 All Elements in Formula: Arsenic, Iron
 IMA Status: Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
 To find out more about this mineral at minDat's website, follow this link   Löllingite

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.545. 'Loellingite'

Frondel, Clifford (1972). The minerals of Franklin and Sterling Hill, a checklist. NY.: John Willey & Sons. p.65

The Picking Table References
 PT Issue and PageDescription / Comment
View IssueV. 41, No. 1 - Spring 2000, pg. 14A Scheelite-bearing Assemblage From Franklin, New Jersey By Robert E. Jenkins II - Löllingite (Small Description)
View IssueV. 31, No. 1 - Spring 1990, pg. 3Breithauptite From The Nickel-Arsenide Assemblage at Franklin, New Jersey, Löllingite (small description)
View IssueV. 10, No. 2 - August 1969, pg. 9Mineral Notes - Loellingite
View IssueV. 7, No. 2 - August 1966, pg. 10The Minerals of Sterling Hill 1962-65 by Frank Z. Edwards - Lollingite

Silver metallic löllingite with calcite Sterling Hill Mine
Silver metallic löllingite mineral, Sterling Hill Mine, near Franklin NJ. Photo by JVF

Löllingite on franklinite from Franklin, NJ
Löllingite (silver) on franklinite (black) from Franklin New Jersey. 2 1/2" x 1 1/2". From the collection of Zack and Ralph Bonard, photo by WP.

All content including, but not limited to, mineral images, maps, graphics, and text on the Franklin-Ogdensburg Mineralogical Society, Inc. (FOMS) website is licensed under a
Creative Commons Attribution-NonCommercial 4.0 International License.
Creative Commons License