Spinel is a magnesium aluminum oxide mineral of the spinel group. Local material is largely unstudied chemically. Palache (1935) reported an analysis with 8.91 wt. % FeO, but questioned its value. It is likely that much of the darkly colored spinel from the marble is partially ferroan, in solid solution toward hercynite.
Spinel is moderately common in the Franklin Marble, was noted by Nuttall (1822), and is in other early lists. Much of the material from here is true spinel, with varying solid solution. The "spinel" so-labeled from the zinc orebodies is largely gahnite. The name ceylonite was used by the analyst Vogel (Palache, 1935), and ceylanite was used by Fowler (1825) and by Torrey, who also used the name pleonaste (Thomson, 1828).
Local spinel occurs as predominantly idiomorphic crystals; massive material is uncommon. The crystals are mostly octahedral with dodecahedral modifications; the cube form is rare. Crystals are commonly 2-6 mm in size, but have been found in cm-sized euhedra, and large crystals are known. The color of local spinels varies from gray to green, pink, and blue; grayish hues are the most abundant, and blue or pink is the most aesthetic. The luster is vitreous. There is no discernible fluorescence in ultraviolet, and no other physical data have been obtained. It is easily recognized by its octahedral habit, hardness, and associations.
Spinel is found throughout the extent of the Franklin Marble and is locally found associated with calcite, corundum, phlogopite, rutile, chondrodite, meionite, and other minerals. Spinel also occurs as masses of crystals with interstitial calcite, but it is predominantly idiomorphic. Rhodonite is a commonly associated mineral in specimens occurring near the zinc orebody. Frondel (1972) reported spinel replaced by corundum. Local spinel-bearing assemblages are largely unstudied.
Large crystals, up to 17 cm, have been found near Sparta and in the Franklin Marble in New York. (Dunn, 1995)

 Location Found: Franklin and Ogdensburg
 Formula: MgAl2O4
 Essential Elements: Aluminum, Magnesium, Oxygen
 All Elements in Formula: Aluminum, Magnesium, Oxygen
 IMA Status: Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
Fluorescent Mineral Properties

 Shortwave UV light: Weak cherry-red
 Mid wave UV light: Weak cherry-red
 Longwave UV light: Moderately bright to weak cherry-red
 Additional Information: Fluoresces best at longwave
 To find out more about this mineral at minDat's website, follow this link   Spinel

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.583

Frondel, Clifford (1972). The minerals of Franklin and Sterling Hill, a checklist. NY.: John Willey & Sons. p.78

The Picking Table References
 PT Issue and PageDescription / Comment
V. 58, No. 1 - Spring 2017, pg. 18Fluorescent Minerals of Franklin and Sterling Hill, N.J., Part 2, Richard C. Bostwick - Spinel
V. 57, No. 1 - Spring 2016, pg. 17Aluminum-Rich Mineral Assemblages at Lime Crest Quarry, Sparta Township, New Jersey, Warren Cummings
View IssueV. 27 No. 2 - Fall 1986, pg. 9Minerals of the Franklin Quarry, Philip P. Betancourt, Spinel Group (spinel?)
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