Two thumbnails from the type locality! Yellowish white, stubby prismatic crystals thomasclarkite-(Y) to 2 mm in albite with green-black, acicular crystals of aegirine and small, white, acicular, pearly adamite-(Y). Thomasclarkite-(Y) is a complex hydrated rare earth carbonate found only in the alkaline intrusive complex at Mont Sainte-Hilaire, Quebec. The mineral is named in honor of Thomas Henry Clark who was a geology professor at McGill University in Montreal, Quebec. Ex. Paulo Matioli collection.