Canadian Rockhound: Collecting at Mont St-Hilaire in 1997

Collecting at
Mont Saint-Hilaire
in 1997
By László and Elsa Horváth

A report of this type is always problematic and some degree of personal bias is unavoidable, as we must rely on our own collecting experience and whatever information we obtain from others. In this year end report, we will cover as much as possible all the minerals found, large and small with special emphasis on rare and new species and minerals new for the locality. One of the problems in the assessment and reporting of the finds is the many sources of information, and what is considered by individual collectors as interesting, significant and noteworthy. One tends to remember only a few salient events or finds, but what may be an interesting find for one person may not be so for others. We keep a detailed collecting log, and for the first time last year, we have kept a species list of the minerals found. Our sources of information apart from our own collecting include Gilles Haineault, the only professional collector here, as well as other local collectors, and in addition to verbal information provided we had a chance to look at a great deal of the material collected by them during the year. This was supplemented by the many keen micro collectors from the eastern USA and Ontario, who attended the field trips. This report is the summary of what we have heard, seen and collected. We have no illusions however, that all the interesting finds came to our attention.

Winter 1996

For the proper coverage of 1997 collecting year, we must look at the early winter collecting of 1996, as many of the rockpiles from which we collected in the spring, were actually quarried in November and December 1996. In November and December (the first snow only came a few days before Christmas), part of the level 7 bench (level 8 is the lowest bench) in the central part of the quarry, a number of successive blasts exposed some very significant pegmatites. Long time collectors may remember the pegmatite pipe that produced the magnificent serandite, analcime and mangan-neptunite crystals in the summer of 1973. This pegmatite, which we would like to call the "Bouhelier pegmatite" after the collector who first found it, was exposed by one of the blasts, and more very good serandite and excellent behoite crystals were found. Another pegmatite opened was an enormous lens shaped, cave like cavity, 7 m long 2 m deep (what was left in the wall) and up to 1.5 m wide. This pegmatite however, did not live up to its impressive size and produced one very large (football size) aggregate of analcime and serandite, eudialyte crystals up to 3 cm, some with an interesting catapleiite alteration, and mangan-neptunite crystals up to 2 cm long. Unfortunately, the blast blew out a lot of the contents and damaged most of what was left in the cavity. A number of smaller pegmatites were also exposed, and one of these yielded what are the best reticulated aggregates of behoite ever found, with exceptional aggregates up to 2 cm across and individual crystals up to 1 cm long. The same pegmatite also had very unusual thin, tabular serandite crystals, and aggregates consisting of divergent sprays of hexagonal prismatic pseudomorphs up to 10 cm long filled with tiny ancylite-(Ce) crystals and a thin shell of what appeared to be rhabdophane-(Ce). Another pegmatite that was opened in the winter, and was still visible in the quarry wall in the spring and summer, yielded exceptionally sharp catapleiite pseudomorphs after eudialyte up to 3 cm in diameter, sprinkled with superb, transparent, brown mangan-neptunite crystals. Associated with these pseudomorphs were exceptionally nice transparent, pink to raspberry red blocky to tabular petarasite crystals. A lot of the petarasite was in the albite lining of this pegmatite and specimens were collected nearly all summer from various rockpiles and the quarry floor.

In addition to these finds in exposed, in situ pegmatites, many other minerals were found in the various rockpiles from blast-obliterated pegmatites, including some excellent serandite crystals up to 13 cm long, associated with rhabdophane and natrolite.

In December, from the eastern end of the quarry some exceptionally sharp and very unusual star-shaped (six pointed star of David) twinned groups of eudidymite crystals were collected. We have not seen this habit before at MSH, but these groups are similar to the platy eudidymite from Mount Malosa, in Malawi. This material was also around in the early spring and summer.

1997

April

Local collectors opened some large altered pegmatites in the eastern end level 8 and found some interesting pseudomorphs of analcime, calcite, natrolite after some unknown precursors. From the various rockpiles in the central part of the quarry level 7, pegmatite material with behoite, excellent nenadkevichite (pink crystals forming sceptres on an earlier generation of pale orange nenadkevichite), gaidonnayite and rhabdophane-(Ce). A few very interesting and unusual miarolitic cavities were found which were densely lined by acicular crystals of lorenzenite up to 2 cm long.

May

A large pegmatite dike was exposed on level 8 in the south corner (Poudrette end of the quarry) and from small cavities in the banded contact of the pegmatite and hornfels a whole array of interesting minerals appeared. The more interesting species included excellent groups of gobbinsite, corundum (pale yellow to blue crystals), hercynite (new), ferrocolumbite (new), schorl (new), röntgenite-(Ce) and many others. From a breccia zone on level 7, superb blue leucosphenite crystals up to 5 mm were also collected.

June

From a small pegmatite vein in the south corner, fan-shaped aggregates of rounded "daisy petal" like thin, plates of lanthanite-(Ce) were found. Associated with the lanthanite-(Ce) were petersenite-(Ce), calcioburbankite, garronite, zircon, gaidonnayite (replacing aegirine) franconite, elpidite, siderite, albite and UK91. Later from another vein in the same area, rich specimens of petersenite-(Ce) (up to 1 cm), calcioburbankite, garronite (crude octahedra 2-4 mm in diameter) and a few UK93 were collected.

A new blast in the extreme eastern wall of level 8 exposed some large marble xenoliths and igneous breccia. The breccia produced yellow narsarsukite and large amounts of lorenzenite (neither of these particularly good). From the marble xenoliths the usual suite of minerals including pectolite, superb tabular fluorapophyllite, and some exceptionally nice sodalite variety hackmanite crystals perched on pectolite crystals were collected. From a the marble xenolith cavity a surprising find of epididymite, elpidite, quartz and pectolite was notable.

July

In early July, in the south corner, collectors exposed a series what became known as the "cryolite holes," consisting of a series of interconnected cavities in a large pegmatite dike (the Poudrette pegmatite). These cavities yielded a very unusual hydrothermally altered and replaced mineral assemblage. The cavity fillings consisted mostly of rod-like pseudomorphs of albite and natrolite up to 15 cm long, with considerable quantity of cryolite as masses up to 10 cm across and crude etched crystals up to 5 cm. Other minerals in these cavities included the best specimens of sabinaite crystals, gobbinsite, chabazite, neighborite, dawsonite, analcime (including cubic crystals), nordstrandite crystals and many others. From the hornfels on level 8, druses of exceptionally good colorless and brown (colored by inclusions) gypsum crystals with individual crystals up to 1 cm were collected. These gypsum crystals were very well formed and largest we have ever seen. From the same area in the hornfels beryllonite, hematite and an unidentified REE carbonate mineral have also been collected.

August

On level 8, in the south corner, a new blast exposed a very interesting cavity in the "Poudrette pegmatite" which yielded one of the most significant finds in 1997. It contained very interesting and unusual cone-shaped clusters of tightly packed, divergent, prismatic elpidite crystals. The simple basal pinacoid terminations formed a lustrous spherical surface, similar to the leifite balls found in 1988. The elpidite crystals are very clean, vitreous and translucent, and the largest clusters are up to 6 cm in maximum dimension. In the same cavity, exceptionally large pseudomorphs consisting of albite-quartz and natrolite after aegirine were also found. These pseudomorphs were very sharp with good teminations, and occurred as individuals or divergent groups up to 20 cm long, many with complex and in some cases distorted dark smoky quartz crystals up to 5 cm long perched on them. Sprays of hexagonal prismatic pseudomorphs up to 5 cm long, consisting mostly of ancylite-(Ce), very good donnayite-(Y) groups and other carbonate minerals were also found.

In the fourth week of August another series of hydrothermally altered and replaced pegmatite cavities were opened by Gilles Haineault and the Horváths. These were rather similar to the "cryolite holes" opened in July, except for local variations in the mineral assemblage. These cavities were essentially filled with pseudomorphs, and produced the best and richest specimens of horváthite-(Y), sabinaite, gobbinsite and synchysite-(Ce) pseudomorphs to date. Horváthite-(Y) occurred as very pale pink to beige clusters of stacked tabular crystals, with exceptional clusters up to 1 cm long. Sabinaite was also abundant as really superb crystal groups, and gobbinsite was found as druses on some specimens covering areas of up to 10 cm². Rod like pseudomorphs reported from the "cryolite holes" up to 20 cm were the most common as were synchysite-(Ce) pseudomorphs up to 10 cm long, and sharp, blocky pseudomorphs consisting of calcite, fluorite, horváthite-(Y), rhodochrosite and possibly other minerals. Cryolite, dawsonite (mostly white powdery masses) were locally abundant.

On level 7, in the central area of the quarry a new blast exposed a zone of cavity rich igneous breccia which yielded cordylite-(Ce), leucosphenite, andradite, eudialyte and tuperssuatsiaite.

September

A fresh blast on level 7, south corner, exposed a pegmatite from which nice specimens of rhodochrosite of an attractive red color with crystals up to 1 cm, elpidite and smoky quartz were collected. From the same blast good specimens of UK93 and petersenite-(Ce) were also collected. During September, a small pegmatite was opened in the floor of level 7, in the central part of the quarry and some nice leucophanite, large analcime, serandite and epididymite crystals were found.

October & November

There was a new blast on level 8, in the nepheline syenite near the ramp, but the rockpile was totally barren. On the same level from the old rockpile (blasted in Sep.) some nice gaidonnayite, nenadkevichite and UK93 were found. The first snow effectively ended the collecting year in the second week of November.

Conclusion

Was it a good year? For most of the local collectors it was an excellent year. It also had to be a good year for those attending the May, June and July field trips. Many different species have been found during the year, the list of species found by the Horváths for 1997 stood at 112 species with at least 10 additional uncertain or unidentified species. Some specimens found represent the best quality, largest crystals and the richest specimens for the species. These include sabinaite, garronite, gobbinsite, cryolite, horváthite-(Y), gypsum, petarasite (pink), corundum, ferrocolumbite (new), hercynite (new), schorl (new), röntgenite-(Ce) and behoite; many others were found as excellent specimens such as petersenite-(Ce), mangan-neptunite, lanthanite-(Ce), synchysite-(Ce), lorenzenite, serandite, rhodochrosite, elpidite, quartz, catapleiite, sodalite, pectolite and others. This was definitely the year of pseudomorphs. In 28 years of collecting we have not seen the quantities and the incredible variety of pseudomorphs encountered in 1997.

Six species new for MSH were added to the list in 1997, they are: lanthanite-(Ce), röntgenite-(Ce), ekanite, hercynite and ferrocolumbite and schorl. Six new species, horváthite-(Y), lukechangite-(Ce), normandite, caresite, charmarite and quintinite have been published, and two new species have been approved by the CNMMN of IMA (UK61 and an analogue of lemoynite). Yes indeed, 1997 was an excellent collecting year at MSH, and we can only hope that 1998 can, if not match it, come close to it.

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