Twinning in alstonite is ubiquitous, forming pseudohexagonal groups. The mineral has one imperfect cleavage and it breaks with an uneven fracture. It is not very hard, with a Mohs hardness of just 4 to , a little harder than fluorite, and its specific gravity is 3.70. It is soluble in dilute HCl and it is not radioactive. The trimorphs alstonite, paralstonite, and barytocalcite all have similar physical properties.
