Hydrotalcite, a magnesium aluminum hydroxide hydrate mineral, was described from Franklin by Dunn (1979c); it has not been reported from Sterling Hill. It occurs as 1 mm, tabular, whitish, hexagonal crystals which are very soft and flexible. It is fluorescent in longwave ultraviolet with a whitish-yellow response color. It is associated with gahnite, hodgkinsonite, calcite, willemite, and serpentine; calcite and hydrotalcite are the last minerals to form. Semiquantitative microprobe analysis found Mg and Al as major cations, with traces of Mn and Zn; carbonate was indicated by effervescence in HCl, and the identity was confirmed by X-ray diffraction.
Another Franklin occurrence, associated with zincite in a vein assemblage, consists of yellow-brown, bronzy, platy crystals in curved aggregates. These are in an intimate mixture of hydrotalcite, hemimorphite, hauckite, and calcite. (Dunn, 1995)

 Location Found: Franklin and Ogdensburg
 Year Discovered: 1842
 Formula: Mg6Al2(OH)16[CO3] · 4H2O
 Essential Elements: Aluminum, Carbon, Hydrogen, Magnesium, Oxygen
 All Elements in Formula: Aluminum, Carbon, Hydrogen, Magnesium, Oxygen
 IMA Status: Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
Fluorescent Mineral Properties

 Longwave UV light: Cream, moderate brightness
 To find out more about this mineral at minDat's website, follow this link   Hydrotalcite

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.621

The Picking Table References
 PT Issue and PageDescription / Comment
View IssueV. 57, No. 2 - Fall 2016, pg. 20Fluorescent Minerals of Franklin and Sterling Hill, N.J., Part 1, Richard C. Bostwick - Hydrotalcite
View IssueV. 33, No. 2 - Fall 1992, pg. 11The Check List of Franklin-Sterling Hill Fluorescent Minerals - Hydrotalcite (Fluorescent Info)
View IssueV. 20, No. 2 - September 1979, pg. 5Contributions to the Mineralogy of Franklin and Sterling Hill New Jersey, Hydrotalcite (small article)
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