The great similarity which exists in the crystallographie and optical constants, cleavage, and absence of twinning in the isomorphous rhombic sulphates is especially marked in Barytes and Celestine, but though the combination of forms is sometimes the same, yet up to the present time a marked individuality has bees perceived in Celestine crystals which has made it easy to recognise the one mineral from the other.

The crystals of Celestine from near Bristol in the red marl, those associated with sulphur from Sicily, or the large flat more or less bluish tabular crystals from Strontian Island, Lake Erie, are varieties which are seldom if ever mistaken for Barytes.