Any yellow to silvery white, fluorescent mica like crystals attached to specimens of other Mont Saint-Hilaire specimens are probably polylithionite. Polylithionite is certainly not one of the more well know mica minerals. Polylithionite, like other micas, has a layered structure of lithium aluminum silicate sheets weakly bonded together by layers of potassium ions. These potassium ion layers produce the perfect cleavage. Polylithionite's rarity, associations with other rare minerals, attractive color and fluorescent color and crystal habit make it an ideal collection mineral.
Color is colorless, white, bluish, greenish, yellow, brown, pink, silvery to pearly white.
Luster is pearly to waxy. Transparency crystals are transparent to translucent. Cleavage is perfect in one direction producing thin sheets or flakes. Fracture is not readily observed due to cleavage but is uneven. Hardness is 2 - 3.