Contributions & Acknowledgements

This article is a collaboration between Cliff Trebilcock, Fred E Davis, and Harold Moritz. Cliff Trebilcock provided the inspiration by finding material at the Fisher Quarry resembling schernikite. He is the source of Maine specimens included in this article (where credited) and he contributed the information on the Fisher Quarry, his finds from there, and other information about Maine mineralogy. The Fisher Quarry is on private property and all specimens were collected with the kind permission of the owner. Specimens were analyzed by Dr. Stefan Nicolescu, mineral collections manager at the Yale Peabody Museum, using the Raman spectrometer at Yale University’s Dept. of Geology & Geophysics. This critical contribution is gratefully acknowledged. Fred E Davis provided comparative analyses of the Raman spectrographs, compared the results to a database of Raman spectrographs of similar minerals, and provided graphics of these results. He also dug up the old Bowman (1902) article used as a critical reference here. Harold Moritz contributed the photographs of specimens from the Gillette Quarry and from Maine (where credited), the schernikite specimen from Gillette for analysis, and wrote and prepared the overall article.

Background

The Gillette Quarry is a granite pegmatite in Haddam Neck, Connecticut, USA that was quarried mainly for microcline intermittently from 1895 until 1944. It is well known for the abundance of miarolitic cavities that produced thousands of euhedral crystals of mostly green elbaite crystals, as well as quality smoky quartz, albite (and cleavelandite), microcline, beryl variety morganite, fluorapatite, and topaz crystals, among other species such as lepidolite and muscovite. Schernikite is a very rare variety of muscovite mica that is abundant at the Gillette Quarry and until now was only known from there. It is a white to pink, fibrous form that contains a little bit of lithium (not enough to qualify it as lepidolite, aka, trilithionite-polylithionite series, and is colored by a dash of manganese (as is lepidolite). It is named for Ernest Schernikow, one of the earliest operators of the quarry in the 1890s. It occurs in two habits at Gillette:

1) As inclusions in quartz crystals. The muscovite starts at a pin point in the quartz crystal’s interior and becomes a divergent sub-parallel bundle of fibers as it reaches the surface where it is often the preferred site for a cookeite hemisphere. Below are fibrous schernikite crystals inside a smoky quartz crystal.



2) As parallel growth assemblages or as overgrowths on lepidolite prisms (sometimes with a core of muscovite) with the fibers arranged longitudinally and parallel to the long axis of the lepidolite prism. The fibers are rhombic in cross section and are in parallel or twin-position so that the rind of fibers and inner lepidolite/muscovite (if present) can be cleaved as if a single crystal. Externally, these assemblages can look like a piece of wood, especially when stained by iron hydroxides. Below are examples with and without a lepidolite core.



Bowman (1902) described and analyzed schernikite in detail where he mentions how the fibers are rhombic in cross-section and fit together exactly parallel without leaving any spaces (tessellated),



The size of the rhombic units varies from easily to barely visible with the naked eye. This feature can be readily seen in the micro photo below of Gillette material.



At that time, schernikite was unknown from any locality other than the Gillette Quarry. Bowman (1902) mentions that he did look for additional specimens from other localities:



The fact that similar if not the same mineral variety potentially occurs in Maine has been out there for 110 years, but in a now rather obscure publication. Had Maine mineral collectors been familiar with schernikite (few people even in Connecticut are because Gillette has been closed to collecting for at least a generation) its identification there might have happened much earlier. But the Bowman paper lends support for it.

Recent Intriguing Finds in Maine

The Fisher Quarry is a granite pegmatite located in a group of similar pegmatites trending NE/SW through Topsham, Maine (see King and Foord, 1994). The quarry operated from approximately 1900 to 1918 primarily for feldspar. In 1929 Ben Burbank found a pocket near the floor of the abandoned quarry that contained dark blue tourmaline, etched topaz and hydroxylherderite crystals. The hydroxylherderite crystals were some of the largest in the world at that time and indications of a larger pocket below aroused the interest of the Harvard University mineralogical museum. In 1932 the museum received permission for Dr. Charles Palache to open the pocket and do a study of the minerals found there. The results are published in Palache (1934) and Palache and Gonyer (1940).

In 2002 collector Cliff Trebilcock received permission from the owner to re-open the Fisher Pocket and to do some collecting and exploration of the ledge in the area. He found a small pocket a few feet from the Fisher Pocket that contained cleavelandite, dark blue elbaite, smoky quartz crystals and an unknown, pink, fibrous mineral with micaceous cleavage. At the time he thought it was an unusual form of lepidolite, more pink than lavender. In 2012 Cliff noticed the schernikite photos from the Gillette Quarry on Mindat.org that appeared to be visually identical to his unknown Fisher Quarry specimens.

Below are two photographs of typical specimens of the unknown, pink, fibrous and micaceous mineral Cliff Trebilcock found at the Fisher Quarry in 2002. The upper photo is a partial crystal (with cleavelandite) viewed parallel to the fibers and perpendicular to the micaceous cleavage. Below it is a group of aggregates of parallel fibers. The tessellated, rhombic cross-sections of the parallel fibers are apparent in both specimens.



Analyses

As shown in the above photographs, the Fisher Quarry specimens appear visually very similar to Gillette Quarry specimens, especially the tessellated habit of rhombic parallel fibers. However, analyses were needed to confirm that the Fisher Quarry material is in fact not another mica species such as trilithionite-polylithionite. Stefan Nicolescu, the mineralogy collections manager at the Yale Peabody Museum, kindly conducted Raman spectroscopic analyses for the authors. This technique works by exciting molecular bonds in a sample with a laser and recording the resulting light given off by the excited bonds. Every material reacts in a unique way to the laser light and the resulting spectrum of unknown material can be compared to a database of spectra from known materials. The vertical axis represents relative intensity of the light given off by the specimen. The horizontal axis values are generally referred to as “wavenumbers” calculated from the excitation wavelength (532 nm for our data) and the Raman spectrum wavelength. The units are expressed as cm-1 or “inverse centimeters.”

Database spectra of muscovite, trilithionite, and polylithionite were obtained for an initial baseline comparison to the schernikite spectrum. Lepidolite has vanished from the species list and along with it any Raman spectra that may have existed. However, because it is just a variety of muscovite, schernikite is also not in the database, so Raman spectra of a sample of known Gillette Quarry schernikite and of suspected schernikite from the Fisher Quarry specimen were obtained by analysis

Below is a comparison of the spectra of muscovite, trilithionite, and a sample of schernikite from the Gillette Quarry. Poylithionite is not included for graphical clarity and because trilithionite showed a closer match to muscovite, though there is much variability in the spectra of these two "lepidolite" micas. All three spectra are generally similar, as expected because they are all in the mica group. Recall that schernikite is a variety of muscovite and so it should have the same spectrum as the latter mineral. Indeed, the muscovite and schernikite peaks are similarly shifted to the right to slightly longer wavelengths compared to the trilithionite. These results support Bowman’s 1902 wet chemical analyses showing that schernikite is a variety of muscovite, not a member of the lepidolite series.



Below are Raman spectra of Gillette Quarry schernikite and the suspected mineral from the Fisher Quarry found by Cliff Trebilcock. Comparison of the two spectra shows that they are nearly identical, the peaks are at the same wavenumbers and there are only slight differences in the intensity of a few of them.



While all the mica spectra are similar, the most remarkable result is the nearly identical spectra from the Gillette and Fisher specimens. These analytical results confirm what is visually apparent, that schernikite indeed occurs at the Fisher Quarry in Topsham, Maine.

Conclusion

The recognition of schernikite in at least one Maine pegmatite opens the door to its presence at other lithium rich pegmatites in the district. Indeed the tantalizing observation by Bowman (1902) of potential schernikite on a specimen from Auburn, Maine is supported by the specimen below from the Greenlaw Quarry, Auburn, Maine possibly collected in the 1940s by Merle Brown. The two views show the tessellated rhombic cross-sections on the cleavage faces and the parallel-growth fibers along the outside of the prism. This specimen was labeled as lepidolite and although not yet analyzed it obviously resembles the analyzed schernikite specimens and is unlike lepidolite (trilithionite-polylithionite).



According to Cliff Trebilcock, local collectors have found similar material they calll "sericite", a term for a fine-grained white, pale green to oily greenish scaly mica and clearly not appropriate. A review of lepidolite and muscovite photographs on mindat.org from lithium-rich Maine pegmatite localities revealed one potential example of schernikite from the Bennett Quarry, Buckfield, Maine.



But generally there are few photos of these minerals posted to Maine pegmatite localities. Some others show tantalizing similarities, but the critical features are either not present or are not visible in these photographs as taken:



We invite their owners to compare these and other interesting Maine micas specimens to schernikite and perhaps re-photograph them to better show features of that mineral variety, if present. Based on Cliff Trebilcock’s experience, other localities for schernikite may include:

Maine Feldspar Quarry and Pulsifer Quarry, Auburn
Berry-Havey Quarry, Poland
Dunton Gem Quarry and Crooker pegmatites, Newry
Tamminen Quarry, Greenwood

There may be many schernikite specimens found in various Maine pegmatites over the decades that are potentially misidentified or overlooked and we implore collectors to examine their collections for them.

References:
Bowman, H. L. (1902): On an Occurrence of Minerals at Haddam Neck, Connecticut, USA. Mineralogical Magazine: 13(60): 97-122.
Palache, C. (1934): A Topaz Deposit in Topsham, Maine. American Journal of Science: series 5: 27: 37-48.
Palache, C. and Gonyer, F. A. (1940): Microlite and Stibiotantalite from Topsham, Maine. American Mineralogist: 25: 411-417.
Scovil, J. A. (1992): Famous Mineral Localities: the Gillette Quarry, Haddam Neck, Connecticut. Mineralogical Record: 23(1):19-28.
King, V. T. and E. E. Foord. (1994): Mineralogy of Maine, vol.1.

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