Luster is vitreous to pearly. Transparency crystals are commonly translucent. Crystal System is trigonal. Crystal Habits include small rhombohedral crystals that have angles close to 90 degrees, making them pseudocubic. Also found commonly as crusts.
Cleavage is perfect in three directions forming rhombs.
Fracture is conchoidal. Streak is pale yellow. Best Field Indicators are its crystal habit, radioactivity, fluorescence and associations.