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 In materials science, polymorphism describes the existence of a solid material in more than one form or crystal structure. Polymorphism is a form of isomerism. Any crystalline material can exhibit the phenomenon. Allotropy refers to polymorphism ...

cavansite Cavansite, whose name is derived from its chemical composition, ''calcium vanadium silicate'', is a deep blue hydrous calcium vanadium phyllosilicate mineral, occurring as a secondary mineral in basaltic and andesitic rocks along with a variety o ...

. Pentagonite was first described in 1973 for an occurrence in

Lake Owyhee State Park Lake Owyhee State Park is a state park in the U.S. state of Oregon, administered by the Oregon Parks and Recreation Department. Bighorn sheep The bighorn sheep (''Ovis canadensis'') is a species of sheep native to North America. It is named fo ...

, Malheur County, Oregon. It has also been reported from the Pune district of India. It occurs as fracture and cavity fillings in tuff and basalt. It occurs with

, heulandite, stilbite, analcime, apophyllite and

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

References

Phyllosilicates Orthorhombic minerals Minerals in space group 36 Vanadium minerals {{silicate-mineral-stub