The anhydrous substance readily absorbs water forming pentahydrate and octahydrate.

At elevated temperatures, it gradually loses water and becomes more whitish.

The octahydrate crystals are optically biaxial, with refractive index components of nα = 1.5399, nβ = 1.5494 and nγ = 1.5607.

[3] Crystals of octahydrate can be grown from solution obtained by dissolving wet Pr2O3 powder with sulfuric acid.

This procedure can be optimised by adding a few evaporation/dissolution steps involving organic chemicals.