The form is such that hardness measurements are impossible and basically irrelevant. The crystals not only look like wool they feel like wool as well. Erionite's structure has a typical zeolite openness 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 erionite can act as a chemical sieve, allowing some ions to pass through while blocking others.
Color is colorless or white.
Luster is vitreous. Crystals are transparent to translucent. Crystal System is hexagonal. Crystal Habits is limited to wool-like aggregates and crusts. Hardness is unknown.