Corundum, an aluminum oxide mineral, was first reported from the local area by Vanuxem and Keating (1822b) and Fowler (1832). It is found in the Franklin Marble.
Corundum occurs, for the most part, as euhedral to subhedral crystals, but deformed crystals, as well as crystals whose shape is inherited in part from contact minerals, are common.
The morphology of local corundum was described and illustrated by Palache (1935), who also noted that crystals occur up to 5 inches (13 cm) in size; cm-sized crystals are more common. The habits vary from equant, to barrel-shaped, to steeply dipyramidal. Most if not all corundum crystals occur rock-locked, not in vugs, and many specimens result from partial dissolution of the enclosing marble matrix, either by weathering or by intentional etching away of the surrounding calcite.
The color of local corundum is variable; much is blue or bluish gray, and violet and fine red material is also known. Color zoning may be present, but inconsistently. The luster is vitreous, and parting is sometimes present. Red corundum has a moderate red fluorescence in longwave ultraviolet; it is weak in shortwave. No physical or optical measurements have been made on local corundum, nor any chemical studies.
Corundum occurs throughout the local extent of the Franklin Marble and close to but not within the orebodies. Few notes were kept, and the quantity and quality of corundum likely varied from quarry to quarry. Palache (1935) reported it associated with spinel, rutile, graphite, pyroxene, garnet, titanite, and phlogopite. Spinel and phlogopite are very common associated minerals. Early collections have some fine corundum specimens. Much corundum has been found in the vicinity of Sparta, and some of this has been mislabeled as having come from Franklin. Replacement of spinel by corundum was reported by Frondel (1972), and some corundum alters to mica locally.
Abundant corundum was found in the Franklin Marble immediately adjacent to the Sterling Hill orebody, associated with phlogopite, rutile, arsenopyrite, gahnite, and other minerals (Dunn and Frondel, 1990) and described herein under margarite. This material was locally abundant. Many specimens do not show the whole assemblage. Fine corundum specimens were found in the debris of the Sterling Hill hemimorphite pits, likely derived from the marble by weathering. (Dunn, 1995)

 Location Found: Franklin and Ogdensburg
 Formula: Al2O3
 Essential Elements: Aluminum, Oxygen
 All Elements in Formula: Aluminum, Oxygen
 IMA Status: Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
Fluorescent Mineral Properties

 Shortwave UV light: Moderately weak red
 Mid wave UV light: Moderately weak red
 Longwave UV light: Moderately bright cherry-red
 Additional Information: Fluoresces weakest at shortwave
 To find out more about this mineral at minDat's website, follow this link   Corundum

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.589

Frondel, Clifford (1972). The minerals of Franklin and Sterling Hill, a checklist. NY.: John Willey & Sons. p.52

The Picking Table References
 PT Issue and PageDescription / Comment
View IssueV. 57, No. 2 - Fall 2016, pg. 15Fluorescent Minerals of Franklin and Sterling Hill, N.J., Part 1, Richard C. Bostwick - Corundum
View IssueV. 57, No. 1 - Spring 2016, pg. 17Aluminum-Rich Mineral Assemblages at Lime Crest Quarry, Sparta Township, New Jersey, Warren Cummings
View IssueV. 45, No. 1 - Spring 2004, pg. 10The Art of Fluorescent Mineral Photography, With Special Attention to the Minerals of Franklin and Sterling Hill Photographing the More Popular Franklin and Sterling Hill Fluorescent Minerals - Corundum
View IssueV. 33, No. 2 - Fall 1992, pg. 10The Check List of Franklin-Sterling Hill Fluorescent Minerals - Corundum (Fluorescent Info)
View IssueV. 32, No. 1 - Spring 1991, pg. 9An Uncommon Margarite/Corundum Assemblage From Sterling Hill, New Jersey, Pete J. Dunn, Clifford Frondel, Corundum (small description)
View IssueV. 27 No. 2 - Fall 1986, pg. 5Minerals of the Franklin Quarry, Philip P. Betancourt, Corundum
View IssueV. 18, No. 1 - March 1977, pg. 23The Fluorescent Minerals of Franklin and Sterling Hill, NJ by Richard C. Bostwick - Corundum
View IssueV. 13, No. 2 - August 1972, pg. 12The Fluorescent Minerals of Franklin/Ogdensburg Area by Frank Z. Edwards - Corundum (Fluorescent Info)

Corundum crystals in franklin marble matrix, Franklin Quarry, FranklinCorundum crystals in franklin marble matrix, Franklin Quarry, Franklin under longwave UV Light
Corundum crystals in franklin marble matrix, Franklin Quarry, Franklin, NJ. Photo by JVF.
Corundum crystals in franklin marble matrix, Franklin Quarry, Franklin, NJ under longwave UV light. The corundum fluoresces bright red and the marble is non-fluorescent. Photo by JVF.

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