SLEUTHING FOR FERRIERITE AND A SMILE ON MY FACE

 

I am continuing my project of sorting out minerals, mainly in Perky Boxes, that I have accumulated in the last few years. I am always a sucker for purchasing small collections of obscure minerals or from somewhat forgotten collecting localities. Recently I hit the jackpot on both accounts by dredging up a Box containing “ferrierite” with a collecting locality listed as Unspecified Ferrierite occurrence (1), North Side of Raymond Peak, Raymond Peak, Silver Mountain Mining District, Alpine County, California. Well, ferrierite is a rather uncommon zeolite, described in 1918, with a Type Locality on the north shore of Kamloops Lake, British Columbia. It took another 50 years until other occurrences of “ferrierite” started to show up in the professional record. It was not until 1976 that Wise and Tschernich determined “ferrierite’s” composition by analyzing nine samples, all from different locations. These determinations noted that either Mg, Na, and K can all dominate the cation composition: “ferrierite can crystallize from solutions with a wide variety of alkali and alkaline earth cations, none of which are non- essential to the zeolite.” This evidence led later researchers (Coombs and others, 1997) to specify that “ferrierite” is not a mineral but a Subgroup and part of the Zeolite Group. Ferrierite-Mg, with magnesium as the dominant cation, is the new name for the Type material from Kamloops Lake. Ferrierite-K is the potassium-dominant mineral although most specimens also contain significant amounts of sodium. Ferrierite-Na is a sodium-dominant mineral and is quite rare in the rock record. In 2021 ferrierite-NH₄ was recognized as an ammonium-dominant, new Subgroup mineral. Unlike the other Subgroup minerals that are associated with volcanic rocks, ferrierite-NH₄ was found in open coal pits in the Czech Republic. In reading these many scientific papers, starting with Wise and Tschernich and ending with the NH₄ papers, it became evident that visual recognition of ferrierite minerals is a difficult identification problem for an ole plugger like me.

And mow for the sleuthing. I was stumped with the composition of my specimen as it simply was identified, by the unnamed collector, as “ferrierite near Markleeville, Alpine County, California.” So, that tidbit at least gave me a start. The not so good news was that none of the named specimens of ferrierite noted in MinDat localities had any connections with Alpine County, California. By luck, probably, I clicked on Ferrierite Subgroup and it listed occurrences of all specimens of “ferrierite” and there it was: “Unspecified Ferrierite occurrence, Alpine County, Silver Mountain Mining District, etc.”  Unfortunately, there was not a specified mineral name listed; however, the location was hot linked and so off I go. That new web site did not tell me much but did indicate a specified location “SSW of Markleeville” and had a great photo of a collected specimen of a Ferrierite Subgroup mineral that really looked like my specimen.

 Knowing that fact took me back to the Wise 1976 American Mineralogist article to rescan for additional clues. What I found was that the Silver Mountain, California, specimen sampled by Wise noted that magnesium was by far the most common cation compared to sodium and potassium. Although I have some difficulty in understanding these chemical analysis charts, this result would seem to indicate that my specimen is Ferrierite-Mg. Still looking for a reference to back up my conclusion, I found Lauf’s 2014 book Collector’s Guide to the Zeolite Group and was happy to read “Other locales for the Mg-dominant material include:.. Silver Mountain, California.” For me, this moment was a time for relief and dinner (seeing it was 9:30 PM and I had turned down my invitation for a 5:30 sit down with my spouse and daughter).  But it was a time of intense satisfaction for my best learning often occurs when I feel like a bloodhound on the trail. I did not have the slightest idea that this rather insignificant mineral would lead me down so many dead ends. However, I could just feel something in my mind that told me to keep after it, dinner could come later!

I am learning all the time. The tombstone will be my diploma. Eartha Kitt.

As for the nitty gritty specifics, Ferrierite-Mg is a zeolite, and these minerals often confuse me (easy to do). They are usually defined as microporous aluminum silicates with unusual properties. Their framework is composed of linked tetrahedra consisting of four oxygen ions surrounding a cation. This arrangement leaves open pores and channels of fixed sizes, and these vacancies allow small molecules to pass through while sieving out larger molecules. One can’t really see these pores but structural analyses can be performed by Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD).

Many zeolites are very siliceous looking with a vitreous luster, often beautiful crystals, and usually remind me of some other mineral! They can be quite confusing, at least to me. When I look at cavities in basalts or tuffaceous sedimentary rocks and see small siliceous crystals lining the vugs  I can call out “zeolite” but that is about it for identification. I am a little better with the large crystals found in Indian basalts, but generally speaking I would be better off sticking to Paleozoic brachiopods. 

Ferrierite radiating crystals. Top FOV ~4 mm. Bottom ~5 mm.

Ferrierite-Mg was the “type” ferrierite described in 1918 from Kamloops Lake, BC.  At this locality most of the crystals are orange to orange red in color. However, in other localities the Orthorhombic crystals are transparent to translucent, soft (-3.0 Mohs), colorless to white, vitreous laths. Most ferrierite-Mg crystals occur as radiating groups.

This has been an interesting exercise in following leads, meeting dead ends, retreating, and following new leads until a final determination is reached. And then, a sigh of satisfactory relief.  

The goal in life is to live young, have fun, and arrive at your final destination as late as possible, with a smile on your face. Jon Gordon

REFERENCES CITED

Coombs, Douglas S., and others, 1997, Recommended nomenclature for zeolite minerals; report of the Subcommittee on Zeolites of the International Mineralogical Association, Commission on New Minerals and Mineral Names: The Canadian Mineralogist, vol. 35, no. 6.

Wise, William S., Tschernich, R. W. (1976) Chemical composition of ferrierite. American Mineralogist, vol. 61, nos. 1-2.