Magnesiochromite

specimen number:
2262125

location:
Black Lake, Thetford Mines, Quebec, Canada

description:
Black grains of magnesiochromite throughout matrix. Good example for the species.

Thetford Mines, located in the Eastern Townships of Quebec, Canada, is a world-renowned mineral district situated within the Thetford Mines Ophiolite Complex. Geologically, this area represents a slice of ancient oceanic crust and mantle that was obducted onto the North American continent during the Ordovician Taconic Orogeny, resulting in massive bodies of serpentinized ultramafic rocks. Magnesiochromite, a magnesium-iron-chromium oxide belonging to the spinel group, occurs here as an accessory mineral or in concentrated pods within the dunite and peridotite sections of the ophiolite, typically forming dark, metallic grains or small octahedral crystals. Historically, mining and quarrying activities in the region were dominated by the extraction of chrysotile asbestos, which was first discovered in 1876 and led to the establishment of several large-scale open-pit operations that defined the local economy for over a century. These operations, including the famous British Canadian and Jeffrey mines, were most active from the late 1800s through the late 20th century before industrial demand declined due to health concerns, leading to the closure of most sites by the early 2010s.

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