IRON ORE. BOUNDARY WATERS, AND BIG FITZ

 How many roads must a person walk down

before you call them a rockhound?  Apologies to Bob Dylan

At one time in my geological past, I organized and led student field trips to the Boundary Waters Canoe Area in Northern Minnesota. Driving north from Hays, Kansas, our group observed and studied various rock units that were unavailable to see in the sedimentary section of western Kansas. For example, we took a good look (and camped) at exposures of the Proterozoic Precambrian Sioux Quartzite (~1.6-1.7 Ga) cropping out around Sioux Falls, South Dakota, and adjacent western Minnesota. These outcrops were a good eye opener for the kiddies since their previous observation of the quartzite was in a pasture in eastern Kansas where I had previously stopped during a paleontology field trip. At this cow pasture locality, the Sioux was observed as small cobbles and boulders, the result of riding down glacial ice during the Pleistocene. The glacier(s) plucked the distinctive pink quartzite from the South Dakota/ Minnesota outcrops and dropped them off in a terminal moraine in eastern Kansas. These two areas presented a great message to help students understand the power of  glaciers.

Sioux Quartzite exposed at the “falls” in the city of Sioux Falls.  Photo courtesy of Steve Dutch, University of Wisconsin.

   

Sources of identifiable glacial erratics found in northeastern Kansas. The dashed line represents the extent of Pleistocene glacier(s) in Kansas.  Map courtesy of Kansas Geological Survey.
 

Boulders and cobbles of Sioux Quartzite in terminal moraine near Wamego, Kansas. Photo courtesy of Kansas Geological Survey.

                 

 Protohistoric Catlinite pipe, probably late 17th century Ioway, from the Wanampito site in Iowa. Public Domain photo from Whittaker and Anderson, 2008, Wanampito: An Early Ioway Site: Newsletter of the Iowa Archeological Society 58(1):4-5.

Near Sioux Falls in southwestern Minnesota is Pipestone National Monument, a national treasure often overlooked by travelers zooming along on nearby I-90. At the Monument the Sioux is also exposed but contains significate layers of catlinite, AKA pipestone. Catlinite is not a formally recognized mineral, although it often appears as such in popular culture, but is a sedimentary rock named argillite. The rock at Pipestone represents tightly indurated “mudstone/claystone” that was formed between layers of the quartzite and subjected to deep burial where heat and compression lithified the clay into an argillite. At Pipestone there are specific minerals present in the argillite that give the rock a diagnostic chemical signature: kaolinite, muscovite, diaspore, hematite, and pyrophyllite. Although the sand quartzite is extremely hard at ~ 7.5 (Mohs), the catlinite is very soft at ~2.5. That softness then allows the argillite to be cut and carved into Native American pipes. The staff at Pipestone believe that “for over 3,000 years, Indigenous people have quarried the red stone at this site to make pipes used in prayer and ceremony - a tradition that continues to this day and makes this site sacred to many people.”

The town of Pipestone also offers an opportunity to observe numerous buildings constructed in the late 1800s and early 1900s of the pink quartzite. The architecture of these buildings is fantastic and well worth a walking tour. The Museum at Pipestone noted that quarried rock was used in building construction in Minneapolis, Sioux Falls, Detroit, Sioux City, Chicago, Kansas City, Omaha and other locations.

The Pipestone City Hall was constructed in 1896. Today it is home to the Pipestone Historical Society who furnished the photo.

North of the Twin Cities the group was able to observe, for the first time, the Mesoproterozoic Precambrian (~1.1 Ga) rocks of the Midcontinent Rift Zone (MRZ), the southern arm of a Triple Junction spreading center near Lake Superior. The MRZ is best known for the large-scale native copper deposits in the Keweenaw Peninsula of Michigan.  

The Midcontinent Rift System or Zone cuts across the North American Craton, the stable center of the continent, that begin to split apart (think East African Rift Zone) starting ~1.1 Ga. Around 20 Ma the rifting stopped and started to close, hence the geological term "failed rift."  The location of the rift south of Lake Superior in Minnesota (south of the Twin Cities), Michigan, Wisconsin, Iowa, Nebraska, and Kansas is inferred from gravity and magnetic data. Public Domain map and info from USGS.

Basalt flows associated with the MFZ exposed along the St. Croix River at Interstate State Park, near metro St. Paul.

Hull-Rust-Mahoning Open Pit Mine near Hibbing is a National Historic Landmark. Photo is Public Domain courtesy of  McGhiever.
 

Further north in Minnesota we took a gander at the giant Mahoning-Hull-Rust Iron Mine near Hibbing (home of Bob Dylan born Robert Zimmerman).  The Mine is located in  the Mesabi Range, one of four iron ranges in Minnesota, the others being the Cuyuna, Vermillion, and Gunflint. The term range refers to a linear feature rather than a topographic high. Rocks of the ranges are Proterozoic Precambrian in age and are the result of the erosion of older Precambrian rocks that were a part of the geologically complex Churchill Craton. Marine waters occupied a large, passive, continental margin of the Churchill  known as the Animikie Basin that accepted (2.5-1.8 Ga) erosional debris consisting of large amounts of silica (quartz etc.) and iron-rich minerals and happened to coincide with a massive change in the composition of the atmosphere known as the Great Oxidation Event (GOE).  The earth’s early atmosphere was a reducing atmosphere with little oxygen and consisting mostly of nitrogen and carbon dioxide that were probably derived from volcanic events. Somewhere in the Proterozoic, questionably as early as 3.5 Ga, photosynthetic cyanobacteria, with chlorophyl, begin replacing the anoxygenic life forms of the reducing environment. The GOE refers to the massive oxygenic time around 2.4 Ga when the chlorophyll-based photosynthesis of cyanobacteria released oxygen as a byproduct. At this same time massive amounts of silica and ferrous iron (Fe2++)was being transported into the Animikie Basin and hitting the oxygenated oceanic waters that oxidized the iron into insoluble ferric (Fe3+++) iron that combined with the silica to form the famous banded iron formations (BIF). Around 1.88 Ga supracrustal BIF rocks of the Animikie were thrust northward to their current localities in the Iron Ranges.The BIF were the sources of the ores fueling the massive iron mining industry. In the Mesabi Range the BIF were close to the surface and hence the concentration of large open pit mines.       

 

The Iron Ranges of Lake Superior. Photo Public Domain courtesy of W.F. Cannon (USGS).

As the high-grade BIF iron ores became depleted in the mid-20^th century mining engineers developed the “taconite process” whereby  low grade ore (termed taconite)   was crushed to a fine grain and the magnetite was removed by magnets, mixed with a bonding agent, usually bentonite, and then wetted, rolled and concentrated into marble size “balls” which were then hardened by subjection to high heat. At that point the taconite contains about 70% iron and heads to one of four taconite shipping ports in Minnesota (Duluth-Superior, Taconite Harbor, Two Harbors, Silver Bay) where it is shipped to the steel mills of Indiana and Ohio. Currently there are only about a half dozen iron ore mines operating in Minnesota; all are in the Mesabi Range. The taconite process is fascinating to observe, and I was pleased to get the class into a personal tour.

The most famous taconite freighter on the Lake was christened in 1958 as the Edmund Fitzgerald and was a monster: 729 feet long and weighing ~13,600 tons. On November 9, 1975, the Big Fitz, with a full load of taconite pellets and a crew of 29, left the Port of Superior, Wisconsin, headed to the steel mills near Detroit, Michigan. Unfortunately, the Big Fitz steamed into a stormy Lake Superior and on November 10 broke apart and capsized in winds at least 90 mph and wave swells of 25-30 feet. All aboard perished and today the ship and crew rest in ~530 feet of water not far from Whitefish Bay. The 1976 disaster was immortalized by Gordon Lightfoot’s recording of the immensely popular folk ballad, The Wreck of the Edmund Fitzgerald.

Upon leaving the iron ranges the class started experiencing a high level of excitement as we headed to Ely, home of the canoe outfitter. My mind begins to fade a little here and unfortunately my maps are still buried “somewhere” after my move. I do remember that we put in at Lake One heading counterclockwise, canoed to the Canadian border near Ensign Lake, canoed down the big Moose Lake, and finished after six days of paddling. Little did the kiddies, on that first trip, know that I had never been in the Boundary Waters previously and was sort of flying by the seat of my pants, my Brunton compass, and my maps. We did miss a few portages the first time, managed to escape most bears, brewed morning coffee that tasted fantastic, and had the time of our lives. Forty years later I periodically run into a student who canoed with me and has stories for their grandchildren. And the kiddies learned much about igneous and metamorphic rocks, how faults may define some lakes, and how other lakes are the result of Pleistocene glaciers scooping out large, and small, basins.

Boundary Waters: quiet and loud.

Now for the mineral, I have a specimen from the Thunderbird Mine in the Mesabi Range near the mining town of Eveleth. Today the property is owned by Cleveland-Cliffs Inc. and is named the United Taconite Mine and includes the former Thunderbird Mine North (TBN) and the Thunderbird Mine South (TBS), collectively the Thunderbird Mine of earlier literature. The Thunderbird is one of the few large open pits still operating in Minnesota. According to Cleveland Cliffs, magnetite-bearing taconite is currently the principal iron-bearing rock of economic interest on the property. In line with other Superior-type iron formations, magnetite-bearing intervals within the Biwabik Iron Formation occur as laterally extensive, stratiform intervals. Economically mineable magnetite occurs exclusively within granular iron-formation (cherty) units of the Biwabik. The ore is sent approximately 10 miles by rail to the concentrator at the Fairlane processing facility in Forbes, Minnesota, to produce a magnetite concentrate, which is then delivered to the on-site pellet plant. From the plant site, pellets are transported by rail to a ship loading port at Duluth, Minnesota.

The specimen I have for this posting is minnesotaite, an iron silicate and really not much to look at. I spent a very few bucks for the specimen due to the facts that: 1) the mineral was named for the State of Minnesota and that is not a common naming practice; and 2) J.W. Gruner (1944), the naming author, first described it as an “iron talc” Fe²⁺₃Si₄O₁₀(OH)_2. That tidbit intrigued me so I took it home and then noted that talc [Mg₃Si₄O₁₀(OH)₂] is a hydrated magnesium silicate while minnesotaite is a hydrated iron silicate and therefore they are isostructural with each other. As best I can tell, there is no substitution between minnesotaite and talc due to the differences in the ionic radii in the two cations (I "think" but don’t always trust my thinking).

Steel gray masses of amorphous Minnesotaite in matrix

Top width FOV ~9.0 mm; bottom FOV ~ 3.0 mm.

Minnesotaite is tough to physically describe since it often is a fine grained, greenish-gray (may appear almost black), massive “blob”. It really does not have much of a luster or shine although MinDat calls it resinous, waxy, or greasy. Some specimens evidently have tiny radiating crystals or platy forms. I might have expected an iron mineral to be quite hard; however, minnesotaite is very soft at maybe ~1.5 (Mohs), about the same as it’s isostructural relative, talc. It is always associated with the Banded Iron Formations.

In retrospect, canoeing the Boundary Waters was much more interesting than examining the iron minerals of northern Minnesota. My memories are quite valuable to me as they are lifelong mementos, something like treasured souvenirs of an interesting journey.

REFERENCE CITED

Gruner, John W., 1944, The composition and structure of minnesotaite, a common iron silicate in iron formations: American Mineralogist, vol. 29, nos. 9-10. Pgs. 363-372. 

RIP Big Fitz

In a musty old hall in Detroit they prayed
In the Maritime Sailors' Cathedral
The church bell chimed 'til it rang twenty-nine times
For each man on the Edmund Fitzgerald

 

The legend lives on from the Chippewa on down
Of the big lake they call, 'Gitche Gumee'
Superior, they said, never gives up her dead
When the gales of November come early

`                               Gordon Lightfoot.

MINERAL ABBREVIATIONS (SYMBOLS)

 

I presume that most rockhounds are serious users of Mineral Database and have noted that descriptions of minerals now include Mineral Symbols. MinDat states, “as of 2021 there are now IMA–CNMNC approved mineral symbols (abbreviations) for each mineral species, useful for tables and diagrams. Please only use the official IMA–CNMNC symbol.” For example, pyrite (FeS2) has a symbol of Py while the potassium feldspar microcline (K(AlSi3O8) has a symbol of Mcc. Warr (2021), in defining the naming process stated, “this contribution presents the first International Mineralogical Association (IMA) Commission on New Minerals, Nomenclature and Classification (CNMNC) approved collection of 5744 mineral name abbreviations…{that standardize} abbreviations by employing a system compatible with that used for symbolising the chemical elements.” The Commission also continues to approve symbols for new minerals as they are officially described. For example, in 2023 112 new minerals were approved. The American Mineralogist, on a regular basis, publishes articles listing, and briefly describing a few, new minerals appearing in the published record and approved by IMA. The latest listing that I could locate was a December 01, 2024 issue [American Mineralogist (2024) 109 (12): 2173–2175.] stating, “This issue of New Mineral Names provides a summary of the newly described minerals from May to August 2024, including karlseifertite, vegrandisite, touretite, auropolybasite, cuprozheshengite, calcioveatchite, and jianmuite.”  A total of 29 new minerals were approved by the IMA-CNMNC from May to August 2024.

The American Mineralogist is the flagship subscription journal of the Mineralogical Society of America; however, the issues containing New Mineral Names, is a free issue. Use your browser to search for New Mineral Names to find the appropriate articles. 

As of mid-July 2024, there are over 6000 valid minerals listed by the IMA! How are ole plugger rockhounds like me supposed to make sense of these thousands of minerals plus the new yearly additions? I have six suggestions/comments: 1) I don’t know the exact number but there are less than one hundred common rock forming minerals and learning about these is not an onerous proposition; 2) make MinDat your favorite web site; 3) most rockhounds will never have the opportunity to observe newly discovered  minerals. Almost all new minerals need electronic gizmos located in research laboratories to validate their existence and many are organic or post-mining minerals; 4) consider subscribing to professional journals, of which there are many. I certainly cannot afford several subscriptions but have found University libraries to be a fantastic reference source, and some public libraries subscribe to popular journals such as Rock and Minerals, Rocks and Gems, and Mineralogical Record; and 6) if your local rock club has a mineral study group, sign up and attend the meetings.

Finally, if you are interested in seeing the official 2021 mineral list with their symbols just scan this QR Code:

 

WORMS, A BLOOD MOON, AND MERCURY

 

As I write this article on Thursday the 13^th of March, 2025, my mind keeps wandering to the celestial event of the month—the Worm Moon, a Full Moon. The name, according to the Old Farmer’s Almanac, is due to warming soil and the appearance of worm casts or even the appearance of earth worms. But hold on, up here in the Northland the temperature may be a tad too cool for earthworms in mid-March. Does 22 degrees F sound like earthworm nirvana? So, a couple of more appropriate names for the March moon is Crow Moon since Poe’s favorite bird is very busy cawing and telling the country that Spring is on the way. That certainly seems the case in our plethora of trees around here. In northern Wisconsin the native Ojibway refer to the March moon as Snow Crust Moon. Sounds good as 40 degrees during the day tends to melt snow while 22 degrees at night freezes it over and a crust forms.

 No earthworms on the 19th!!

But the big event is that this a Full Moon is also a Blood Moon, a total lunar eclipse—and it was a dandy. In this arrangement the moon, earth, and sun are lined up and the earth’s shadow begins to creep across the moon until the moon is completely covered, but is still visible. What happens is that the earth’s atmosphere scatters some sunlight across the lunar surface and at “totality” the moon appears a copper red or even a blood red. Really spooky but also a spectacular event.

Here in the Northland, sometime shortly after 11:00 CDT the earth’s shadow started to creep across the moon, slowing getting larger and larger until totality was reached about 1:30 AM. I observed the process until about 2:00 AM but totality lasted until about 2:30 AM when the earth’s shadow started to withdraw. The “neat” thing about the event is that we were in a short term, major  warming event in Wisconsin, so I was able plop myself on the porch rocking chair with only a light jacket and my binocs and experience this celestial event with a clear sky and quietness. Wow, and double wow, since Thursday the 20^th is the Spring Equinox.

The copper red moon rang a little bell in my head that reminded me of a Perky box containing the mercury mineral corderoite that needed examination. The red connection is not copper related but because many mercury minerals display some sort of a red color.

Although mercury has not been legally mined in the U.S. since 1992, at one time our country had a substantial number of operating mines. Most of these mines were in the far western US (see map) although in terms of production per mine the Terlingua fields in the Big Bend area of west Texas was substantial. I could not easily locate past production figures before 1992. In winding down the lack of mine production, much of  of the production in the early 1990s was from catching mercury as a byproduct in gold mining operations. The U.S. also imported mercury and recovered the metal from recycling efforts. Today the use of mercury in the US has greatly decreased due to its toxicity, environmental concerns, and human health conditions. As noted on the map, most mercury mines were located in California, Nevada, and Oregon. 

Mercury was mined in Nevada from about 1907 (discovered then at Antelope Springs and with mining beginning in 1914) until the early 1990’s. The District mines produced from veins in Triassic limestone, dolomite, conglomerate, and shale (Gray and others, 1969). Evidently these veins were emplaced during the Miocene because of extensional magmatism (Noble and others, 1988).  That is, Miocene extensional tectonics involved the stretching of the earth’s crust producing what we know today as the Basin and Range physiographic province.

Mercury mines in the U.S. None are active today.    Map courtesy of Land Matters, a non-profit 501c3 charitable educational organization found at www.mylandmatters.org.

One of the best-known mercury mining locations of later years was the Cordero--McDermitt Mines, Opalite District, Humbolt County, Nevada. The McDermitt (including the Cordero and other smaller mines) is just one of several mines that are located in the Opalite Mercury Mining District that straddles the Nevada-Oregon State Line,  The District is associated with a volcanic caldera complex where eruption centered around a Miocene age of ~16 Ma (Henry and others, 2016).  The original mercury mineralization was in the Cordero Rhyolite, but later hydrothermal action deposited the metal into nearby lake or stream-deposited tuff (volcanic ejecta) (Henry and others, 2016). Mercury in the caldera complex was first mined in the 1970s and the operations ceased in 1990. The McDermitt complex was the most important mercury producer in the Americas during the 20^th century producing 279,000 flasks to 1988 (geoconsultancy.com.au).  The minerals cinnabar, ~50%, (mercury sulfide HgS) and corderoite, ~50%, (mercury sulfide chloride Hg₃S₂Cl₂) yielded almost all the mercury. However, there are several other mercury minerals present in minor amounts.

Corderoite is another one of those mercury minerals that appeared “later in life” as Eugene Ford and others did not described it until 1974 from the Codero Mine. Of course, the Mine was very new at that point, but the mineral had not been noted at other mercury localities. In addition to corderoite, the Cordero Mine (McDermitt complex) is the Type Locality of these other mercury minerals: alexearlite, kenhsuite, mikecoxite, and radtkeite.

When many rockhounds think of a “standard” color for mercury minerals the bright cherry red of cinnabar probably comes to mind, at least it does for me. Cinnabar was the mineral we always studied in mineralogy courses and little did I know, until decades later, that less abundant (that we did not observe in class) mercury minerals are various shades of pink, orange, silvery-gray, brownish red, yellow, and even colorless. Interestingly, many of these mercury minerals begin to darken, some irreversible, when exposed to light sources as they are photosensitive. In the well-studied photosensitive cinnabar, the first reaction to light, moisture and chloride ions is the change to corderoite:

3HgS + 2Cl à Hg₃S₂Cl₂ + S

Corderoite is  also unstable when exposed to light and oxygen and will degrade to calomel:

Hg₃S₂Cl₂ + 2Cl à Hg + 2S + Hg₂Cl₂

And finally, calomel will degrade into mercuric chloride and metallic mercury (Keune and Boon, 2005; Radepont and others, 2011). These reactions probably seem rather insignificant to rockhounds except to note that most corderoite in the rock record is the result of the degradation of cinnabar. However, to art historians and art conservators the chemistry behind this darkening is extremely important. Vermilion, the red coloring made from cinnabar perhaps as far back as 8000 B.C., was the primary red pigment during the Renaissance Era until the 20^th Century. So, conservators were greatly concerned about beautiful red paints used by the masters (and others) in their majestic works of art darkening with age. Keune and Boon (2005) determined that chlorine salts in the atmosphere were the major culprits in darkening during the degradation of cinnabar into elemental mercury. Museums are now able to restrict moist air and chlorine from reaching the paintings and also to chose specific light frequencies for the gallery illumination (Wogan, 2013).

Cherry red cinnabar degrading to pink corderoite. Matrix is opalite with white quartz and glassy hyolite opal. Bottom width FOV ~ 7mm. Top width FOV ~ 4 mm.

Corderoite is an isometric mineral although individual cubic crystals are quite small, less than 2 mm, and quite rare. Most occurrences of the mineral is as tiny grains, druse-like, on degrading cinnabar. It usually is pink to pink red to orange pink color when fresh but as it also degrades in light and moisture to a gray and finally black color. Meanwhile it remains tough to identify except using the pink color and its relationship to the degrading cinnabar. As noted above, the McDermitt complex has produced corderoite (degrading cinnabar) from both the rhyolitic complex rocks and the original tuffaceous lake sediments which today have consolidated to “opalite” with angular fragments of rhyolite and tuff along with secondary amorphous silica and others. In other words, it usually is not a nice looking rockhound mineral but certainly was a critical mineral in the mining and production of mercury.

Want to know more about mercury? I would suggest the USGS Circular 1248, Geologic Studies of Mercury by the U.S. Geological Survey.

https://clu-in.org/download/contaminantfocus/mercury/geologic-studies-of-mercury-c-1248.pdf

REFERENCES CITED

 

Foord, E.E., Berendsen, P., and Storey, L.O. 1974, Corderoite, first natural occurrence of α-Hg3S2Cl2, from the Cordero mercury deposit, Humboldt County, Nevada. American Mineralogist, vol,.59, nos. 7-8.

Gray, J.E., M.G Adams, J.C. Crock, and P.M. Theodorakos, 1999, Geochemical Data for Environmental Studies of Mercury Mines in Nevada: U. S. Geological Survey Open-File Report 99-576.

 Henry, C.D., Castor, S.B., Starkel, W.A., Ellis, B.S., Wolff, J.A., Laravie, J.A., McIntosh, W.C., and Heizler, M.T., 2017, Geology and evolution of the McDermitt caldera, northern Nevada and southeastern Oregon, western USA: Geosphere, v. 13, no. 4.

Keune, K. and Boon, J.J., 2005. Analytical imaging studies clarifying the process of the darkening of vermilion in paintings. Analytical Chemistry, vol. 77. No. 15.

Noble, D.C., J.K. McCormack, E.H McKee, M.L. Silberman, and A.B. Wallace, A.B., 1988, Time of mineralization in the evolution of the McDermitt Caldera Complex, Nevada-Oregon, and the relation of Middle Miocene mineralization in the Northern Great Basin to coeval regional basaltic magmatic activity: Economic Geology, vol. 83.

Radepont, M., De Nolf, W., Janssens, K., Van Der Snickt, G., Coquinot, Y., Klaassen, L., and Cotte, M., 2011. The use of microscopic X-ray diffraction for the study of HgS and its degradation products corderoite (α-Hg3S2Cl2), kenhsuite (γ-Hg3S2Cl2) and calomel (Hg2Cl2) in historical paintings: Journal of Analytical Atomic Spectrometry vol. 26, no. 5.

Wogen, T., 2013, Mercury’s dark influence on art: Chemistry World at: https://www.chemistryworld.com/news/mercurys-dark-influence-on-art/6735.article.

SLEUTHING FOR FERRIERITE WITH 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 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.