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

  

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.