Museum Astrophyllite is one of the more common and conspicuous mineral species at Mont Saint-Hilaire. It can be found in the nepheline syenite in proximity to various pegmatitic structures, and rarely in hornfels, marble xenoliths and miarolitic cavities. It is practically identical in color and habit to kupletskite, with which it may be intimately associated, rendering visual identification unreliable.
Color is medium to dark brown, reddish bronze or brownish red.
Luster is greasy to pearly. Diaphaneity is transparent to translucent in small crystals, masses are opaque. Crystal Habits include well-formed sharp, tabular to bladed crystals to several cm in length. Bladed and acicular microcrystals may also be found. Fracture is uneven.