Pentagonite is a rare mineral and a member of the Zeolite group. It is very similar in appearance and color to Cavansite. In fact, the two are defined as being dimorphous: describing two minerals that have the same chemical formula but are different in crystal structure. Pentagonite is similarly colored brilliant sky-blue to blue-green color, and its luster is vitreous to pearly. However, it is rarer and more difficult to find than Cavansite. Associated minerals include Calcite, Stilbite, Gyrolite, Quartz and other Zeolites.
The crystal system for Pentagonite is orthorhombic, typically forming small prismatic bladed crystals in radiating clusters, and masses of these clusters. Twinning is common, exhibiting 5-fold symmetry, thus its name. Also forms in cavities, vugs and fractures (this particular form is very aesthetic and provides natural protection for the mineral crystals).
Pentagonite is found in extremely limited localities, including India and the USA (Oregon).