The Mountain Lake cluster consists of two diatremes or volcanic pipes in Northern Alberta, Canada. It was emplaced during a period of kimberlite volcanism in the Late Cretaceous epoch. Although they were originally described as kimberlite or kimberlitic, the Mountain Lake (ML) rocks were later reclassified as alkaline ultramafic volcanics, hybrid alkaline ultramafic rocks, basanite or alkali olivine basalt. Due to extensive clay alteration that obliterated much of their original mineralogy, the question of their proper classification remains unsettled.