Riebeckite, a member of the amphibole group, is fairly rare at Mont Saint-Hilaire. Color is usually grayish blue or grayish green. Luster is vitreous to silky. Diaphaneity is translucent. Crystal Habits include matted or radiating flexible fibers to 5cm.
Fracture is uneven to subconchoidal.
Hardness is 5 - 6. Streak is gray. Associated Minerals include albite, apophyllite series, calcite, eudialyte and pectolite.