Thomsonite is a sodium calcium aluminum silicate hydrate mineral of the zeolite group.
Thomsonite is known from Franklin and Sterling Hill, but is not found in the assemblages in which other local zeolites occur. It was first reported as calciothomsonite Gordon (1923b); this was shown to be thomsonite by Palache (1935). It was also verified from Franklin by Cook (1973). Much material labeled "thomsonite" from Franklin is in fact xonotlite, which occurs in the same assemblage, and is much more abundant. Thomsonite is a very rare mineral locally.
Thomsonite is white to colorless, occurring in clusters of prismatic crystals. The cleavage is perfect, and the luster is vitreous. Thomsonite has a weak white to light yellow fluorescence in both longwave and shortwave ultraviolet (Bostwick, 1982). X-ray diffraction and optical methods are best for distinguishing thomsonite from xonotlite.
Thomsonite has been verified by [Dunn] on one Franklin specimen, on which it occurs as a 2 cm bundle of subparallel, colorless to white, acicular crystals. This is the same specimen verified by Cook (1973) and comes from the part of the mine described by Hurlbut and Baum (1960). Thomsonite occurs in a vug surrounded by prehnite, which is enclosed in a mixture of ganophyllite, unanalyzed mica, and garnet. (Dunn, 1995)

 Location Found: Franklin and Ogdensburg
 Year Discovered: 1820
 Formula: NaCa2[Al5Si5O20] · 6H2O
 Essential Elements: Aluminum, Calcium, Hydrogen, Oxygen, Silicon, Sodium
 All Elements in Formula: Aluminum, Calcium, Hydrogen, Oxygen, Silicon, Sodium
 IMA Status: Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
Fluorescent Mineral Properties

 Shortwave UV light: Weak pale yellow, very rare
 To find out more about this mineral at minDat's website, follow this link   Thomsonite-Ca

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.515. 'Thomsonite'

Frondel, Clifford (1972). The minerals of Franklin and Sterling Hill, a checklist. NY.: John Willey & Sons. p.79

The Picking Table References
 PT Issue and PageDescription / Comment
View IssueV. 58, No. 1 - Spring 2017, pg. 19Fluorescent Minerals of Franklin and Sterling Hill, N.J., Part 2, Richard C. Bostwick - Thomsonite
View IssueV. 33, No. 2 - Fall 1992, pg. 11The Check List of Franklin-Sterling Hill Fluorescent Minerals - Thomsonite (Fluorescent Info)
View IssueV. 18, No. 2 - September 1977, pg. 19The Fluorescent Minerals of Franklin and Sterling Hill, NJ by Richard C. Bostwick - Thomsonite
View IssueV. 13, No. 2 - August 1972, pg. 13The Fluorescent Minerals of Franklin/Ogdensburg Area by Frank Z. Edwards - Thomsonite - variety calciothomsonite (Fluorescent Info)
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