Return to Alkaline Rocks
The Mont Saint-Hilaire intrusive complex about 40 km east of Montréal (Québec, Canada) is well known among mineral enthusiasts as one of the most prolific mineral localities and collecting sites in North America. Mont Saint-Hilaire is part of the relatively young Monteregian Alkaline Province. The bulk of the complex is made up of alkali-gabbroic and foid-syenitic rocks, although most mineralogically interesting are the metasomatized xenoliths of diverse rocks and pegmatite veins exposed in the Poudrette quarry on the northern side of the mountain. As of March 2006, more than 350 mineral species have been recognized at Mont Saint-Hilaire, including 49 minerals for which this is the type locality. More recent updates and further details can be found at the Alkali-Nuts website. Roadmetal from the Poudrette quarry has been used in many places across this part of the country (including the capital), which inspired a witticism that the streets of Ottawa are the largest mineralogical museum in the world. However, thanks to its proximity to Montréal and generosity of its owners, the quarry is also frequented by collectors and enthusiasts. It is, therefore, not surprising that many of the Mont Saint-Hilaire discoveries have been made by amateur mineralogists. Their dedication and continuing efforts to preserve the most unique mineral and rock specimens for science have been acknowledged in the names of petarasite, horvátite-(Y), haineaultite and other minerals christened after the prominent Mont Saint-Hilaire collectors. The mountain is also known for its unique flora, which earned it the status of biosphere reserve in 1978.
[Upper right] Mont Saint-Hilaire (looming at the horizon) and Mont Saint-Bruno (lower and nearer) as seen from the Montréal Tower looking east. The highest point of Mont Saint-Hilaire is about 415 m above the surrounding plain. Both mountains are alkali-gabbroic intrusive complexes of similar Cretaceous age.
[Lower right] Another cheery day of collecting in the Poudrette quarry.
[Below] The eastern part of Mont Saint-Hilaire across Lac Hertel comprises feldspathoid syenites of the so-called East-Hill suite. This shore is the less mineralogically interesting, gabbroic side of the complex.