Pentagonite
Formula: Ca(VO)Si4O10 · 4H2O
Species: Silicates – (Phyllosilicates)
Colour: Greenish blue
Lustre: Vitreous
Hardness: 3 – 4
Specific Gravity: 2.33 (Calculated)
Crystal System: Orthorhombic
Name: For the pseudosymmetrical five-fold habit of the typical pentagonite twins.
Type Locality: Owyhee Dam, Lake Owyhee State Park, Malheur Co., Oregon – USA
Dimorph of: Cavansite. Structurally related to plumbophyllite.
Cavansite might be a low-temperature form and pentagonite a high-temperature form.