Litchfieldite and the Litchfield Sodalite Locality

A short distance from the Kennebec River, in the towns of Litchfield and West Gardiner, and not far fom the village of Purgatory, are deposits of a most unusual rock, an eleolite-syenite, variety *litchfieldite, which has aroused the interests of scientists and mineral collectors for over a century and a half. While in situ* outcrops of litchfieldite are infrequent and not easily accessible, there are a number of readily accessible concentrations of boulders that can provide good samples of the rock, abundant nepheline and cancrinite, and rarely sodalite to the patient collector. Excellent descriptions of the occurrences of the minerals are provided in King and Foord (1994; cancrinite on p. 71; nepheline on p. 251; sodalite on p. 324). Directions to several collecting sites can be found in the Collector's Guide to Maine Mineral Localities (pdf format).

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The first known mention of the deposits occurs in the proceedings of the Sixth Annual Meeting of the Association of American Geologists and Naturalists, held in New Haven, Connecticut, in 1845, where C.T. Jackson (who had just completed the first survey of the geology of Maine in 1837-39) described the minerals and provided chemical analyses of the sodalite (which he unfortunately misidentified as cancrinite) and cancrinite (which he unfortunately misidentified as nepheline) (see King and Foord, 1994, p. 324) (Jackson, 1846).

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These unusual minerals and the rock that hosted them continued to attract the attention of collectors and chemists through the latter half of the 19th century, but it was left to W. S. Bayley, in 1892, to present the first discussion of the distribution and origin of the "eleolite-syenite of Litchfield and other localties in Maine." (Bayley, 1892). In this work he named the rock variety at present known as litchfieldite:

"....Consequently, in spite of the great predominance of albite over orthoclase, we are quite justified in calling our rock an eleolite-syenite [or in more current terminology, a nepheline syenite, as eleolite is a synonym for nepheline, used to describe a massive to coarsely crystalline variety of the mineral - the author] . Its large percentage of albite, however, and its possession of but one bisilicate constituent, and that a biotite (lepidomelane), seem to distinguish it as a very well defined variety of eleolite-syenite, as well characterized in the hand-specimen as in the thin section. Its peculiarities are so strongly marked that the rock seems worthy of a distinctive varietal name, for which no more appropriate one can be found than litchfieldite, derived from the familiar locality - Litchfield - whence nearly all the specimens in museums were obtained."

A more thorough investigation of the "field relations of litchfieldite and soda-syenites of Litchfield, Maine" was left until the field seasons of 1916 and 1917, when R.A. Daly visited the district (Daly, 1918).

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Half a century later, a modern petrologic investigation of the alkalic rocks at Litchfield, Maine, was undertaken by D. S. Barker (1965). Barker identified a suite of rocks ranging in relative age from an older leucosyenite (a rock composed of more than 95-percent alkali feldpar with scant dark minerals - primarily sodic pyroxene and amphibole), through nepheline-free biotite syenite, to a younger nepheline syenite (including the type litchfieldite), and minor younger mafic syenite and albitite pegmatite dikes.

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The rock achieved such notoriety that the town of Litchfield has placed a specimen of litchfieldite on its town seal.

References

Barker, Daniel S., 1965, Alkalic rocks at Litchfield, Maine: Journal of Petrology, v. 6, part 1, p. 1-27.

Bayley, William S., 1892, Eleolite-syenite of Litchfield, Maine, and Hawes' hornblende syenite from Red Hill, New Hampshire: Geological Society of America, Bulletin, v. 3, p. 231-252.

Daly, Reginald A., 1918, Field relations of litchfieldite and soda syenites of Litchfield, Maine: Geological Society of America, Bulletin, v. 29, p. 463-470.

Jackson, Charles T., 1845, On cancrenite, nepheline, elaolite, and zircon from Litchfield, Maine: Association of American Geologists and Naturalists, Proceedings, v. 6, p. 44-49.

King, Vandall T., and Foord, Eugene E., 1994, Mineralogy of Maine Volume 1: Descriptive Mineralogy: Maine Geological Survey (Department of Conservation), 418 p.

Text and photos by Marc Loiselle.

Originally published on the web as the December 2005 Site of the Month.

Last updated on March 31, 2006