Pentagonite is a rare silicate mineral with formula Ca(VO)Si4O10·4(H2O). It was named for the unusual twinning which produces an apparent five-fold symmetry. It is a dimorph.
Pentagonite was first described in 1973 for an occurrence in Lake Owyhee State Park It has also been reported from the Pune district of India. It occurs as fracture and cavity fillings in tuff , heulandite , apophyllite