Zeolites have an openness about their structure that allows large ions and molecules to reside and actually move around inside the overall framework. The structure actually contains open channels that allow water and large ions to travel into and out of the crystal structure. The size of these channels controls the size of the molecules or ions and therefore a zeolite like phillipsite can act as a chemical sieve, allowing some ions to pass through while blocking others. Color is clear, white, yellowish and reddish. Luster is vitreous, also silky on sphericule's surfaces.
Crystals are transparent to translucent.
Sphericules are small tight balls that have a sparkling or silky luster in phillipsite. Aggregates can be radiating, fibrous, columnar and encrusting. Cleavage is imperfect in one direction. Fracture is uneven. Hardness is 4 - 4.5.