Tuesday, April 13, 2021

FUNKY LITTLE ROCK SHOPS WITH NIFTY MINERALS

 Get off the beaten path... If you want to find those mom-and-pop joints, those funky little places, just ask around.    Guy Fieri

Funky little rock shops where everyone wears a mask!

I often bemoan the fact that certain items are disappearing from the American roadside, things like drug stores with ice cream and shakes, general stores, non-chain hamburger stands, and especially “mom and pop” rock/mineral/fossil stores.  I suppose that my age and nostalgic thinking make these disappearances seem severe when in reality you can order any mineral that pops into your mind from a web business (now ice cream is a little tougher).  But there is, to me, something special about pulling open a dusty drawer in an old cabinet and taking a lighted loupe to examine a dusty specimen with old hand-written labels.  I am always on the lookout for these stores and make an attempt to locate and patronize these establishments.  On the other hand, it is tough to make a living selling minerals for a buck or five and most of these stores seem a labor of love.

I recently took a little road trip and stopped at one of my favorite old timey stores and begin sneezing while blowing dust off some of the drawer specimens—not many other tourist patrons bother with the drawers.  Not really needing any new minerals, I still made a purchase of some interesting specimens at “cheap” prices.  So, what little jewels did I come home with (only a partial list)?

The very reason I collect and write about minerals is so I might not sleepwalk through my entire life.    Apologies to Zadie Smith

Bisbee, Arizona, is known to rockhounds and mineralogists through the world.  The Copper Queen Mine and the Lavender Pit Mine have produced an array of secondary copper minerals that are considered classics.  Rock and mineral shows have devoted their attention and themes to Bisbee minerals.  And virtually any mineral collection, at least here in the states has a beautiful specimen of blue Bisbee azurite and usually one of green malachite.  However, I needed something new from Bisbee and spotted a thumbnail with antlerite, a copper sulfate hydroxide [Cu3(SO4)(OH)4].  Antlerite is found as a secondary mineral in the carbonate-poor, oxidized zone at many copper mines but is never common.  In fact, Anthony and others (1995) noted it was rare and in mines of the Bisbee area was collected from the Copper Queen Mine (probably) as small crystals of excellent quality implanted on brochantite.  Antlerite ranges from emerald-green to light green to blackish green in color.  Crystals are vitreous, translucent, brittle and soft (~3.5 Mohs) and leave a pale green streak.  Most crystals are thick tabular, or equant or short prismatic.   They also occur as rather non-descript granules or aggregates of fibrous crystals.


Green crystals of antlerite of various and shape.  Some of the very light green translucent mineral matter may be brochantite.  Width FOV ~4 mm. 

A garnet was one of the standard minerals included in Physical Geology laboratories specimen boxes (along with feldspar, calcite, quartz, etc). Usually, it was a dark colored dodecahedron that was identified by its shape and hardness of ~6+. Students learned that garnets were silicates and created during a metamorphic event.  

By the time mineralogy class rolled around students were introduced to a variety of garnets and learned that “garnet” was not a legitimate mineral name but referred to a group of silicate minerals differing in composition but crystallizing in the same system (Isometric), and their mineral properties such as hardness, cleavage and density were all very similar. Usually the specimens studied were almandine [Fe2+3Al2(SiO4)3], pyrope [Mg3Al2(SiO4)3], spessartine [Mn2+3Al2(SiO4)3], andradite [Ca3Fe3+2(SiO4)3], and grossular [Ca3Al2(SiO4)3]—all end members in the Garnet Group.  Things got more difficult in graduate-level courses in igneous and metamorphic mineralogy/petrology and instructors added uvarovite, also an end member, [Ca3Cr2(SiO4)3] to the list for study. Chemical formulae for members of the Garnet Group is X3Y2Si3O12 where X includes the divalent (2+) oxidation charge cations like Ca, Mg, Fe, and Mn while Y represents trivalent cations (3+) oxidation charge like Al, Fe, and Cr; all cations are clustered around the silica tetrahedra. Today MinDat lists 14 different minerals belonging to the Garnet Group with many of these types having numerous varieties. For example, spessartine has at least six varieties while grossular parades out 15 varieties including the popular, and expensive, green tsavorite with coloring supplied by chromium and vanadium. Garnet Group members have two solid solution series: 1) pyrope-almandine-spessartine; and 2) uvarovite-grossular-andradite. Essentially all colors of the rainbow are present in some variety of garnet since rare blue colored specimens were discovered a couple of decades ago.

At the rock/mineral shop I picked up a small cluster of andradite crystals. This species has three major varieties: melanite (black), topazolite (yellow-green), and the uber expensive demantoid (green).  My find of mineral store garnet crystals is the rather unusual andradite variety termed melanite or titanium garnet.  These are black garnets where the titanium evidently replaced or comingled with the silicon since the titanium (up to ~11%) appears as titanium oxide.  The crystals are dodecahedrons with an adamantine luster and a hardness of ~6.5-7.0 (Mohs), and a white streak.  They are pretty opaque but will partially transmit light from a rear source. Unlike other garnets that usually form in metamorphic environments, melanites with their titanium often form in alkaline igneous rocks (low silica), but also in serpentine, skarns, crystalline schists, and iron ores. The locality information, simply “New Idria Mining District, San Benito, CO, California.”  This District is famous for world class benitoite, neptunite, topazolite and melanite andradite garnets. I believe the garnets formed in a skarn, a metamorphosed limestone intruded by hydrothermal solutions heated by nearby intrusions.




Titanium-rich andradite crystals, variety malanite.  Width FOV Top: ~2.1 cm.; Bottom: ~7 mm.

The Spruce Pine Mining District in North Carolina is one of the best-known mining areas in the U.S.  It is in a beautiful area of the Blue Ridge Mountains centered in Mitchell and Yancy Counties and mineral-wise is famous for gem specimens of beryl--varieties aquamarine, emerald, heliodor, and morganite.  North Carolina is the country’s largest producer of feldspar and original mines centered near Spruce Pine and produced from a Precambrian pegmatite; however, current production is from “alaskite” (a variety of granite) described as a very “coarse-grained, light-colored, feldspar-quartz-muscovite rock. Composition of the rocks averages about 40 percent plagioclase (soda-spar), 25 percent quartz, 20 percent microcline (potash-spar), and 15 percent muscovite” (information gleaned from North Carolina Geological Survey at deq.nc.gov).  The Spruce Pine area is also the major producer of sheet mica, scrap mice and olivine in the U.S., as well as a number of other industrial minerals. 

The specimen I picked up is an intrusive igneous rock with various feldspars, schorl (a black tourmaline), quartz, and a nice golden beryl crystal that was collected from the Ray Mica Mine near Burnsville in Yancy County. I have been through Burnsville a few times on my way to lodging in Little Switzerland, and while traveling along the Blue Ridge Parkway, a scenic 469-mile road running near the crest of the Blue Ridge and connecting Great Smoky Mountain National Park in the South and Shenandoah National Park in the north.  The Blue Ridge is the high part of the Appalachian Mountains with a variety of crystalline rocks emplaced during continental collision and subduction generally termed the Grenville Orogeny or the Grenville Cycle.  At any rate, the Grenville was not one major event but a series of orogenic phases from ~1250 Ma to ~980 Ma, or somewhere around there, with the end result being the formation of the Supercontinent Rodinia.  There were additional granite emplacements somewhere around 700 Ma due to rifting of Rodinia.  The Paleozoic history of the Blue Ridge and the Appalachian Mountains is a “whole nother story.” 


Golden beryl. Top: length ~1.6 cm.; width of hexagonal end ~7 mm.  

Cluster of schorl crystals.  Width FOV ~1.9 cm.

I enjoy it; my experiences in traveling and looking at the rocks have taught me the importance of an open mind and have given me a willingness to wander off the beaten path - not only to keep life interesting, but also to understand in a meaningful way that things do not look the same from every vantage point.               

Apologies to Esther Dyson

REFERENCES CITED

Anthony, J.W., S.A. Williams, R.A. Bideau, and R.W. Grant, 1995, Mineralogy of Arizona: The University of Arizona Press, Tucson.


Monday, April 12, 2021

JACKSTRAWS, CERUSSITE AND ATLAS MISSLES: I"M READY FOR THE TIMES TO GET BETTER

 

Life in the fast lane in Tescott, ca. early 1950s.  Life was good.

As a kid growing up in rural 1940s-50s Kansas “the boys” essentially had the run of the town and created their own “fun.”  No electronic games, no TV, and not much money in the families.  But virtually everyone in town was on the same level and my brothers and I really did not notice much of a socio-economic difference in the population of maybe 396 (that is a stretch), plus numerous dogs, only a few cats (no dog was a “house pet” and they all loved to chase cats), and one yellow canary who laid eggs and pined for a mate. We knew the local bankers had more monetary resources than most, but on the other hand, my family was able to borrow money to keep my father’s business above water. Well, not always above water since the town usually flooded about every five years (and still does).  I always thought the village was a Ford and Chevy (always used vehicles) town with a scattered Mercury or Plymouth and an occasional Hudson, Packard or Studebaker thrown in the mix.  In other words, a non-wealthy small town much like the others in rural farm/ranch Kansas.  Most families had provided a father and/or a brother to World War II and Gold Star mothers proudly hung the medallion in the front window (and grieved for the remainder of their lives). Korea sort of came and went (for a kid) but I do remember the WWII vets talking about the “commie reds” trying to take over the world.  At 10 years old I was too busy climbing trees, swimming in the local ponds, fishing, and trying to blow things up with firecracker powder to think much about the “commies.”

I've got to tell you I've been rackin' my brain
Hopin' to find a way out
I've had enough of this continual rain (substitute any word--shooting, war, virus)
Changes are comin', no doubt

It's been a too long time
With no peace of mind
And I'm ready for the times
To get better
                                                                        Crystal Gayle

I think if you question persons of my age and ask what changed their life as they lost their carefree “kidhood” and moved to adulthood, they will answer “Vietnam.”  I have prefaced numerous other Blog postings about my childhood and college days and will not repeat them.  However, my change was almost immediate—the day they moved the giant Atlas Missile down the highway to a large hole in the ground about a mile from town (Operational Base #10 assigned to 550th Strategic Missile Squadron).  I thought, wow, maybe those “commie reds” really want to “kill us.”  I dreamed about some guy in the Kremlin with a map and a red pin stuck into Tescott, Kansas, noting a hole in the ground there housed a really big missile.  I feared that if those Kremlin boys pushed a button the people in Tescott did not have much of a chance.  I also wondered where our big Atlas was pointed.  Was it aimed at Moscow, or perhaps at a podunk small, rural town in Siberia? Dad didn’t know the answer; however, he was also worried.  And then it all hit, Cuba, eastern Europe, and some unknown jungle in southeast Asia called Vietnam or French Indochina.  Our country is still suffering the effects of that jungle today.  Will it ever go away?  By the way, that ole hole in the ground is still in the pasture covered with some big steel doors—at least that is the rumor.  I think there were 12 of these missile silos surrounding a Strategic Air Command (SAC) base at Salina.

Yesterday is not ours to recover, but tomorrow is ours to win or lose.    Lyndon Johnson

Now, how do all these rattling words connect to geology?  It has been a long story, but I am getting there. As I noted, kids in my small town did not have electronic gizmos to play with and our games were pretty simple—dominos, board games like Monopoly (not my favorite), building “things” with Tinkertoys or Lincoln Logs, and something called Pick-up-sticks or Jackstraws.  If you can imagine a number, 50 or so, of ~9-inch-long colored toothpicks that are held in a “bunch” with one end touching the floor, and then gently released to form a “pile” of sticks, you have the basics of the game!!! Participants tried to remove a single stick without disturbing the others.  Big clumsy hands like mine were not overly successful and my final count was usually low.

I suppose that today’s children would be quite bored with the game—I was!  Jackstraws takes its name from the straws in a scarecrow or child’s doll—individual straws going in many different directions.

In rockhounding and mineralogy the name jackstraw is now applied to long prismatic crystals of several different minerals that appear in sprays or masses in which individual crystals are haphazardly arranged in “every which direction”—a jackstraw aggregate of crystals.  Among the best-known Jackstraw Crystals are orange-red crocoite from the Adelaide Mine, Tasmania, millerite from Halls Gap, Kentucky, stibnite and tourmaline group minerals from a variety of locations, and epidote from the Green Monster Mine, Alaska. However, to most rockhounds the descriptor jackstraw brings up connotations of cerussite from the Flux Mine, Santa Cruz County, Arizona.



Jackstraw cerusssite on limonite/goethite (iron oxide) matrix.  Width FOV Top: 1.2 cm.; Middle: 9 mm.; Bottom: 7 mm. 

Interestingly the Mine is very near Alum Gulch in the Patagonia Mountains, the area that produced halotrichite described in the Posting July 24, 2020. The Flux, at one time, produced copper, lead, zinc silver, manganese, and minor gold from a complex of Paleozoic rocks intruded by Mesozoic igneous rocks, and a Tertiary rhyolite.  I believe most of the mineralization is associated with intrusive dikes and sills connected with both the granite and the rhyolite.  Small scale mining was present in the middle 1800s while larger production centered on 1884-1993.  Claims and ownership have been sort of haphazard since the end of large-scale mining in 1963 and active claims are still present.

The major mineral commodities from the Flux were zinc and lead with the latter entering into the jackstraw picture.  Cerussite is a secondary lead carbonate [PbCO3] most often associated with primary galena [lead sulfide] and anglesite [lead sulfate].  In most instances the galena [PbS] oxidizes to anglesite [PbSO4] and then to cerussite [PbCO3] with exposure to carbonated water.

Cerussite, or white lead ore, has a variety of crystal habits including massive, reticulate, tabular, thin plates, equant, fibrous, prismatic, and others.  The colors are also varied but are mostly colorless and pale pastels and all leave a white streak.  The hardness is ~3.5 while crystals have a greasy to adamantine luster, a conchoidal fracture, and are translucent to transparent.  Because of the lead content the mineral is “heavy” with a high specific gravity (~6.5).  As a carbonate, cerussite will “fizz” in weak hydrochloric acid

The Jackstraw crystals from the Flux Mind are snow white in color and form spiky brittle crystals or very tight parallel bundles in a limonite/goethite matrix. Why do these jackstraw crystals form? I don’t have the slightest idea why. That is one of life’s persistent questions that always are better described than easy answers.

Jackstraw cerussite or the game of Jackstraws is not to be confused with the song Jack Straw by the Grateful Dead!!!

Leavin' Texas, fourth day of July,
Sun so hot, the clouds so low, the eagles filled the sky.
Catch the Detroit Lightnin' out of Sante Fe,
The Great Northern out of Cheyenne, from sea to shining sea.

Monday, March 29, 2021

MORE PESKY MONT SAINT-HILAIRE MINERALS

 Every day brings new choices.          Martha Beck

The previous posting described, sort of, a few sodium-rich minerals from the Poudrette Quarry located on Mont Saint-Hilaire near Montreal Canada.  The area has some very uncommon alkaline-rich igneous rocks that produce a suite of very rare to uncommon minerals. Since I am working with purchased and gifted micromounts, the mineral crystals in the mounts are quite small (many less than one millimeter) and often (most of the time) very difficult for me to identify; however, I am giving it my best to understand as much as possible. 

In youth we learn; in age we understand. Marie von Ebner-Eschenbach

Lorenzenite is a sodium titanium silicate [Na2Ti2(Si2O6)O3] that is usually associated with alkaline magmatic or pegmatitic rocks rich in nepheline and deficient in quartz. The Type Locality of lorenzenite is not at Mont Saint-Hilaire but at another famous outcrop of nepheline syenite pegmatite, the Narssârssuk pegmatite, Narsaarsuk Plateau, Igaliku, Kujalleq, Greenland.  As at Mont Saint-Hilaire, the Greenland pegmatite has produced a number (13) of Type Locality minerals rich in sodium (including elpidite described in the previous posting). I find it interesting that MinDat does not have a photograph of lorenzenite from its Type Locality.

Lorenzenite from the Poudrette Quarry usually appears as acicular needle-like crystals often in sprays (seems to be an atypical habit).  Most are relatively colorless and are transparent to translucent.  However, these Canadian crystals are completely different from large equant and opaque crystals appearing in various darker shades of brown, mauve, blue, and black from localities in the Kola Peninsula in Russia (825 minerals and 248 Types; see posting Nov. 24, 2019) .  Lorenzenite has a hardness of ~6.0 (Mohs) with Poudrette crystals being vitreous to subvitreous while Russian specimens are dull to submetallic.  Poudrette crystals fluoresce a pale yellow to dull green under short-wave ultraviolet light and was a big help in identifying crystals on my specimen. 

Sprays of lorenzenite with a variety of other minerals that remain beyond my reach of identification.  The scattered black crystals in the upper left are submillimeter crystals of anatase, a titanium oxide. Width FOV ~1.0 cm.

Scattered anatase crystals as noted above.
 

 
An enlargement of lorenzenite from above photomicrograph.

Polylithionite is a member of the “Mica Group” and more specifically the Trioctahedral Micas, a family that includes minerals such ass biotite, lepidolite, zinnwaldite, and phlogopite—all silicates where the major cations are potassium or sodium, plus aluminum, magnesium, lithium, iron and perhaps a few others. Polylithionite is a potassium lithium-rich mica [KLi2(Si4O10)(F,OH)2]: Poly=many, Lith=lithium, so much lithium. It is found in alkaline igneous rocks with the mineral Type Locality in a pegmatite exposure, the Ilímaussaq complex, Kujalleq, Greenland (with 11Type Minerals).

Polylithionite crystals show a hexagonal outline and appear to be hexagonal crystals composed of stacked sheets (perfect basal cleavage).  However, they are actually pseudo hexagonal crystals that are colorless, white, gray, violet, or pinkish. All colors are transparent, soft (Mohs 2-3) and have a pearly luster with a white streak. The crystals, mostly tabular, also fluoresce yellow. There is a solid solution relationship between polylithionite, lepidolite, and trilithionite (minerals are determined by the lithium-aluminum ratio). 


 
Crystals of micacous, hexagonal polylihionite embedded in crystals of natrolite.   Width FOV ~1.3 CM.    


Glassy translucent to transparent prismatic crystals of natrolite, some with shallow pyramidal termination. The longest crystals are ~3 mm.

Another sodium aluminum silicate, natrolite, shares my thumbnail  specimen with polylithionite.  Natrolite [Na2Al2Si3O10-2H2O] is a zeolite and more often is found in miarolitic cavities of basalt.  It is related to scolecite (calcium aluminum silicate) and mesolite (sodium calcium silicate) and very difficult for an ole duffer like me to distinguish. Most natrolite specimens for sale at mineral shows or exhibited in museums are long, slender, prismatic, vitreous crystals up to a meter in length.  The Poudrette natrolite crystals are “square shaped along the long C-Axis”, “short” (squat) prismatic crystals rather than needle-like. They have a very shallow pyramidal termination, are translucent to transparent with a measured hardness of ~5.0-5.5. Colors of all crystals range from colorless, white, gray, even to colorful shades of orange, pink, brown to green. As for the environment of formation, MinDat.org states: “[Natrolite crystals] characteristically [are] found in low temperature hydrothermal systems, especially in volcanic and volcanically-derived rocks, but also in a wide range of other rock types, typically feldspathic [like the nepheline syenite found at Mont Saint-Hilaire].” At any rate, the specimen is quite interesting and likely contains other minerals that I cannot identify—above my pay grade.

There is no end to education. It is not that you read a book, pass an examination, and finish with education. The whole of life, from the moment you are born to the moment you die, is a process of learning.          Jiddu Krishnamurti

I have a third specimen labeled serandite which is a sodium manganese silicate [NaMn2Si3O8(OH)].  Mont Saint-Hilaire is famous for producing salmon-orange to salmon-red crystals of serandite with the color, due to manganese, making the mineral somewhat easy to identify.  However, some serandite crystals tend toward brown to pink to colorless and there is a good possibility that the pink crystals are schizolite (sodium calcium manganese silicate). In addition, most of the Poudrette crystals are long prismatic and sometimes bladed.  I studied my thumbnail for what seem like hours trying to locate the distinctive deep salmon-red, long crystals I had seen in professional exhibits—no luck.  In digging into the literature, and examining many photographs, I discovered that some serandite crystals are short, blocky. prismatic crystals, sometimes colorless to light peach/salmon. In opening my mind, I soon “discovered” a nice grouping on my specimen. Serandite crystals are transparent to translucent, have a vitreous to greasy luster, a white streak, and a hardness of 5.0-5.5 (Mohs).  At Mont Saint-Hilaire serandite crystals are found in a sodalite syenite pegmatite composed mainly of microcline, sodalite, and nepheline (Lacroix, 1931in Tarassoff and Horvath, 2019).   For a great history and description of serandite see the Tarassoff and Horvath article.




 
These light peach/salmon crystals are my identification of serandite. I could be wrong.  The longest dimension of any of the crystals is ~ 2mm.

The joy of life comes from our encounters with new experiences, and hence there is no greater joy than to have an endlessly changing horizon, for each day to have a new and different sun.            Christopher McCandless
 

REFERENCES CITED

Tarassoff, P. and L. Horvath, 2019, Connoisseur’s Choice: Serandite, Mont Saint-Hilaire, Monteregie, Quebec, Canada: Rocks and Minerals, vol. 94, issue 4. 

This has been a tedious exercise for me.  I am not a mineralogist, the minerals are tiny and numerous from Mont Saint-Hilaire, most are unfamiliar to me, my digital camera ate several photomicrographs (about 3 times), and I miss my desk computer (this has been completed on a laptop).  But right or wrong the editor said it is going to press!  And the sun is shining, I am safe and well, and my entire family has now received at least the first vax.

The search for knowledge is a long and difficult task.    Fabiola Gianotti

  

Wednesday, March 10, 2021

SODIUM-RICH ALKALINE MINERALS AND A RATTLED BRAIN

I am thinking that the pandemic fatigue finally rattled my fragile brain and caused some neurons to skip a beat.  The pandemic had kept me busy since March and I enjoyed sorting minerals, reading, writing articles, and contemplating future ideas.  And then boom, I received my second Covid vax toward the end of January and a terrific weight seemed lifted from my shoulders.  I really had no desire to do much of anything except look at minerals, read, and eat (all the unhealthy foods)!  And so, my Blog lagged, and postings were nonexistent for about six weeks.  Just not any enthusiasm for putting in the hours needed for a decent entry.  But then, slowly, my mojo started to return.  The days were getting longer (we recently passed the February Snow Full Moon), CSMS scheduled its rock and mineral show (usually in early June) for October 2021, the Rocky Mountain Federation, in conjunction with the American Federation, scheduled their annual meeting and show in Big Piney, Wyoming, for late June, a condensed “Tucson show” by ~80 dealers is scheduled for April, and I confirmed my fall camping reservation in the Black Hills. In addition, I joined the Baltimore Mineral Club and have actively participated in the Zoom meetings (and have made some new long-distance friends) and submitted an article for their newsletter.  But perhaps most interesting is that I discovered Mineral Talks LIVE appearing on Zoom each Wednesday at 1:00 PM EST (11:00 out here in the Mountains).  Each week a mineralogist/rockhound presents a “show and tell” about their collection (like Joe Dorris from the Springs or Alex Schauss from Tucson or Bruce Cairncross from South Africa), or a museum curator/curatrix, or a jewelry designer, or how to photograph minerals (Jeff Scovil).  The series has really perked me up.

Now, I still wear my mask, avoid crowds, stay out of most stores, and am constantly slathering on the hand sanitizer.  My family, friends and acquaintances stayed well and hopefully the worst is behind us (although I plead with persons to practice CDC suggestions), and to get their Vax.  So now, I need to start working on a post or two!

For years, even before I started collecting minerals (rather than fossils) I had “heard” of the famous Poudrette Quarry near Montreal, Quebec.  It was my limited understanding that the quarry produced “lots of” strange minerals; however, it was far away from my home and a quick field trip was out of the question. A few years ago, I purchased a nice mineral, carltonite, at the Tucson show for it beautiful blue color rather than for its collecting locality (Poudrette Quarry).  At about the same time I acquired several specimens needing to be “micromounted” and a few of these were from the Quarry—they were stuck in a drawer and remain unmounted.

After sort of coming out of my funk, I started scanning the internet and reading a variety of mineral and geology articles.  Somehow, I stumbled on a fantastic article about the Poudrette Quarry; that wobble in turn lead me to a mineral drawer where my specimens from Canada reside.  Yep, there were the Poudrette specimens stuck in the back of the drawer (and waiting to be mounted).  I had to take care of these!

GEOLOGICAL ASSOCIATION OF CANADA, MINERALOGICAL ASSOCIATION OF CANADA, 2006 JOINT ANNUAL MEETING MONTRÉAL, QUÉBEC

FIELD TRIP 4A: GUIDEBOOK, MINERALOGY AND GEOLOGY OF THE POUDRETTE QUARRY, MONT SAINT-HILAIRE, QUÉBEC

Charles Normand & Peter Tarassoff

Microsoft Word - GuidebookMSHfinal2-JP2.doc (mcgill.ca)

This field guide is an absolutely fantastic piece of work that nicely explains the intricacies of the geology and mineralogy of the Poudrette Quarry.  But beware, it is not for the faint of heart, those who might struggle with complex geological situations. I have read it several times trying to get a better understanding of Mont Saint-Hilaire—with only modest success.

I have abstracted the following information from this guidebook:     

The Poudrette quarry located in the East Hill suite of the Mont Saint-Hilaire alkaline complex (igneous rocks containing a high concentration of sodium and potassium, more so than in other igneous rocks and therefore containing feldspathoid minerals [lots of nepheline]) is one of the world’s most prolific mineral localities, with a species list exceeding 365 (MinDat now shows 433 valid minerals). No other locality in Canada, and very few in the world have produced as many species. With a current total of 50 type minerals (MinDat now lists 71 Type Minerals), the quarry has also produced more new species than any other locality in Canada, and accounts for about 25 per cent of all new species discovered in Canada.

Mont Saint-Hilaire is a small, roughly circular composite igneous intrusion rising some 375 meters above the surrounding Saint-Lawrence peneplain and measuring 3.6 kilometers in its widest part…The intrusion, physically a monadnock, is part of a series of Lower Cretaceous age intrusions collectively known as the Monteregian Hills.

The Monteregian Hills are related both temporally and chemically to partial melting of lherzolitic (ultramafic igneous rock containing much olivine often originating at about 200 miles deep in the earth’s mantle)  mantle by a rising thermal plume…during the late Cretaceous period. Based on 40Ar/39Ar data...the Monteregian Hills were emplaced during a single episode at about 124±1 Ma.

The mountain is separated into two major units. The western half of the mountain is composed of a concentric succession of a variety of gabbroic rocks which were emplaced first... The eastern half of the mountain, which represents the youngest part of the intrusion, comprises various types of peralkaline syenitic rocks (these rocks, syenites, are coarse grained, like granite, but contain very little quartz and have orthoclase as the dominant feldspar) and igneous breccias (the East Hill suite).

In common with other alkaline complexes, the primary reason for the large number of species found in the quarry is the agpaicity (the alkaline environment described below) of the rocks in the East Hill suite. The highly alkaline environment is characterized by the presence of sodium-rich feldspathoids, feldspars, pyroxenes, amphiboles and zeolites as primary minerals, and complex silicates containing titanium, zirconium, niobium, fluorine, and rare-earth elements (REE).

The specimens that I purchased are all minerals marked as being collected from the Poudrette Quarry.  Although there are a number of former and current quarry names, L.H. Horvath wrote (2019 in Mindat) “I would strongly advise that for now we keep the Poudrette quarry name, as it has been well established in the minds of collectors and in the mineralogical literature for the last 50 years. Furthermore, with few exceptions all the minerals (including recently described type minerals) on the species list below have been collected before 2007” (the year the Quarry was sold and renamed Carrière Mont Saint-Hilaire Quarry). My specimens are all sodium-rich silicates or carbonates with which I was unfamiliar---until I acquired new information after reading the field guide: normandite [NaCa(Mn,Fe)Ti,Nb,Zr)(Si2O7)OF], dawsonite [NaAlCO3(OH)2], and elpidite [Na2ZrSi6O15-3H2O].

The Poudrette Quarry is the Type Locality of normandite (1990), one of those sodium-rich, complex, rare-element silicates containing titanium, zirconium, and niobium along with fluorine that are found in alkaline igneous environments. Normandite occurs as tiny (often), yellow to orange, prismatic or fibrous crystals with a vitreous luster, It is tough to tell but crystals are transparent to translucent and have a measured hardness of 5-6 (Mohs).  My specimen containing normandite seems to be a dark gray nepheline syenite; however, that may be an erroneous guess.  The major mafic mineral in the syenite is some type of an amphibole with a nice bronze sheen under LED microscope lights.  My initial guess was aegirine, a pyroxene; however, the cleavage planes are closer to the 120 degrees typical of the amphiboles.


These photomicrographs of normandite, along with the black amphibole, are the best my camera could produce.  The yellow orange spot in the top is actually a cluster of tiny acicular crystals about .2 mm long (1/5 of a millimeter or about 1/64 of an inch).  In the second photo the longest crystal is about .3 mm long.
 

Elpidite is a hydrated sodium zirconium silicate occurring as a low temperature secondary hydrothermal mineral.  The prismatic crystals have a range of” pastel” colors; however, those on my specimen are sort of a dull white with a silky luster.  The crystals form in sprays or bundles although at times they are solitary. The mineral has a measured hardness of ~5 (Mohs) and diaphaneity ranges from opaque to translucent.  The crystals in my specimen are found as sprays/bundles in small cavities/vugs in a groundmass of ?albite/microcline.  Although the specimen is a small thumbnail, it contains a number of tiny minerals that my limited mineralogical skills will not allow me to identify!



Elpidite crystals in vugs: top, width of vug ~1.0 mm; middle, width of vug ~ 4.5 mm; bottom, width of vug ~2.0 mm.
 

Dawsonite is not a silicate like the previous two sodium-rich Poudrette minerals but is a low temperature, hydrothermal, sodium aluminum carbonate hydroxide.  At Mont Saint-Hilaire dawsonite is associated with the weathering of aluminum- and nepheline-rich rocks (feldspathic dikes and syenite). However, I first saw dawsonite as an authigenic mineral collected from the Eocene greater Green River lake sediments in Utah, Wyoming, and Colorado.  It was associated with alkaline oil shales and Smith and Milton (1966) noted that in some specimens dawsonite makes up ~25% by weight of the shale, contains ~35% of acid soluble Al2O3, and was viewed as a potential source of aluminum.  I completely forgot about dawsonite after completing that long-ago course in sedimentary petrology.

Cluster of prismatic dawsonite crystals.  Width FOV ~5.0 mm.
 

At the Poudrette Quarry dawsonite is mostly colorless to white, soft (~3 Mohs), transparent and leaves a white streak.  It has more of a silky luster that, at times, grades to vitreous, and forms encrustations or “clumps” of acicular or bladed crystals or tuffs of crystals.  Some dawsonite, at least in my specimen, effervesces in dilute HCl.

So, there it is, a measly three specimens from 433 known minerals from the Poudrette Quarry.  I can’t imagine what a collection of 400 or so must look like.  In fact, I really don’t know how many different minerals the largest Poudrette collection contains.  I am also unaware if collecting is still permitted.  I have read that no collecting is allowed, or that highly restricted collecting is sometimes permitted for a local rock club.

WORD OF THE DAY: agpaicity as in the agpaicity of the rocks in the East Hill suite.  Merriam-Webster: Definition of agpaite: any of a group of feldspathoid rocks (such as naujaites, lujauvrites, or kakortokites) from Ilimausak, Greenland, which differ from normal nephelite-syenites in having alumina in excess of the alkalies.  Merriam-Webster also noted that users of agpaite must love words since the only definition is in the unabridged dictionary.

At the next CSMS meeting, I will send a mineral specimen to any member that uses the noun or adjective in a grammatically correct sentence!  

 

REFERENCES CITED

Smith, J.W. and C. Milton, 1966, Dawsonite in the Green River Formation of Colorado: Economic Geology, v.61, no. 6.