Feldspathoids are commonly found in silica-poor igneous rocks, where analcime is sometimes present as well. Analcime is sometimes placed in the feldspathoid group since its chemistry and occassional occurrences are similar. Analcime's structure however has a typical zeolite openness about it that allows large ions and molecules to reside and actually move around inside the overall framework. The structure contains large 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 analcime can act as a chemical sieve.
Color is clear, white or gray, with greenish, yellowish and reddish tints possible.
Luster is vitreous. Also granular and massive. Cleavage is absent. Fracture is uneven. Hardness is 5 - 5.5.