| Mont Saint-Hilaire |
 Mont St. Hilaire is located some 40km east of Montreal in the Rouville region of Quebec. The Poudrette and Demix quarries are found in what is called a pluton or intrusion. A pluton is formed when the magma, or melted rock, hardens under the surface of the earth. Pluton minerals are typically coarse grained (i.e. have large crystals), are very resistant to erosion and often associated with volcanoes or igneous intrusions. The Mont St. Hilaire pluton now rises some 350 meters above the much less weather resistant Ordovician limestone of the St. Lawrence lowlands. Odovician limestone is a common ocean sediment that has hardened into rock and dates back to between 505 to 438 million years. This location has become a world famous collection site because it yields at least 250 different mineral species. Most sites only offer half a dozen or so minerals. Some of the species at Mont St. Hilaire are only found in a handful of places around the world, while others are, as of yet, found only in Mont St. Hilaire and nowhere else on earth! Interestingly, the quarries at that location are (or were) in operation for the sole purpose of producing crushed rock for road metals and concrete. It is, however, these quarry operations that exposed these fabulous minerals. Minerals are formed when magma begins to cool and solidify, and the longer the cooling process, the larger the minerals. As mentioned, Mont St. Hilaire was formed from magma cooling underground which therefore occurred at a very slow rate and resulted in very well formed minerals in great abundance. Some of the minerals for which Mont St. Hilaire is famous are serandite, catapleiite, leucophanite, carletonite, leifite and analcime.A very special feature of this location is the fact that the solidified magma created a rock type known as an alkali syenite. An alkali syenite is a plutonic rock that consists of mainly potassic feldspar and plagioclase (two common minerals) and very little quartz. Normally, quartz should be found in relatively high quantities. This igneous complex (i.e. rock formed from melted material) also contains many rare earth elements. It is this lack of quartz and the presence of these rare earth elements that are responsible for the rarer minerals contained in this site. On a global scale, this alkali syenite complex is extremely rare. |
Mont St-Hilaire
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