Zircon



Zircon, a zirconium silicate mineral, was first reported by Vanuxem and Keating (1822b), but it is relatively rare in the ore deposits. It is found at both Franklin and Sterling Hill, but nearly all specimen material is from Franklin, especially from Balls Hill. It occurs sporadically as an accessory mineral, and fine crystals have been recovered.
The morphological description was given by Palache (1935), and little can be added here. Some crystals show three tetragonal dipyramids, some from Balls Hill have as a terminal form, and many are sharp and euhedral. Most Franklin zircon is dark brown, with vitreous luster. Most of the observed crystals are not discernibly fluorescent in ultraviolet; those that are have a weak orange fluorescence in shortwave, and some have been reported to have a weak red fluorescence. Little chemical analytical work has been done on local material; some Balls Hill zircon is Hf-free and has near end-member composition.
The best known specimen of Franklin zircon, described by Cook (1889) and illustrated by Palache (1935, Plate 16-a) as being from Balls Hill, is a fake specimen composed of many crystals glued together. Zircon is found on valid Balls Hill specimens as free-growing, prismatic 5 mm crystals associated with garnet, pyroxene, epidote, and ferroactinolite.
Franklin zircon, although generally sparse, was most common in the pegmatite of the Trotter Shaft area. One fine 2 cm crystal was collected from the calcium silicate units in the Franklin Mine by John L. Baum, Resident Geologist at Franklin.
Zircon is less common in the orebodies; those from the Trotter Shaft are commonly rock-locked in microcline and are brittle, and thus are commonly found in fragments. Fine 2 cm zircon crystals were found with 5 cm andradite and unstudied pyroxene from Franklin; similar crystals are also associated with fluorapophyllite and epidote from the Palmer Shaft. Fine 5 cm crystals have been found associated with rhodonite. Among the most uncommon specimens is one of light pinkish brown, 1 cm, slightly bulging crystals which have gray color in the cores and near the terminations of the crystals; the final growth is of dark brown lustrous zircon.
Zircon was reported and illustrated from the Sterling Hill corundum/margarite occurrence by Dunn (1979c). Here it occurs as tiny crystals, slightly resorbed, in the Franklin Marble, associated with rutile, anorthite, arsenopyrite, goldmanite, and other species (Dunn and Frondel, 1990). (Dunn, 1995)


 Location Found: Franklin and Ogdensburg
     
 
     
 Formula: ZrSiO4
 Essential Elements: Oxygen, Silicon, Zirconium
 All Elements in Formula: Oxygen, Silicon, Zirconium
     
 IMA Status: Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
     
Fluorescent Mineral Properties

 Shortwave UV light: Orange of moderate to weak intensity
 Mid wave UV light: Orange of moderate to weak intensity
     
 To find out more about this mineral at minDat's website, follow this link   Zircon

     
 References:
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.400

Frondel, Clifford (1972). The minerals of Franklin and Sterling Hill, a checklist. NY.: John Willey & Sons. p.85


The Picking Table References
 PT Issue and PageDescription / Comment
V. 58, No. 1 - Spring 2017, pg. 24Fluorescent Minerals of Franklin and Sterling Hill, N.J., Part 2, Richard C. Bostwick - Zircon
View IssueV. 41, No. 1 - Spring 2000, pg. 15A Scheelite-bearing Assemblage From Franklin, New Jersey By Robert E. Jenkins II - Zircon (Small)
View IssueV. 33, No. 2 - Fall 1992, pg. 11The Check List of Franklin-Sterling Hill Fluorescent Minerals - Zircon (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, Zircon (small description)
View IssueV. 30, No. 1 - Spring 1989, pg. 9The Epidote-Pyroxene-Fluorapophyllite Assemblage in the Franklin Mine at Franklin, New Jersey, Philip P. Betancourt, Zircon (small description)
View IssueV. 20, No. 2 - September 1979, pg. 7Contributions to the Mineralogy of Franklin and Sterling Hill New Jersey, Zircon (small article)
View IssueV. 18, No. 2 - September 1977, pg. 23The Fluorescent Minerals of Franklin and Sterling Hill, NJ by Richard C. Bostwick - Zircon
View IssueV. 13, No. 2 - August 1972, pg. 13The Fluorescent Minerals of Franklin/Ogdensburg Area by Frank Z. Edwards - Zircon (Fluorescent Info)
     
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