Mineral
Pentagonita
Ca(VO)Si₄O₁₀·4H₂O · Silicatos (Filosilicatos)
Pentagonite is a rare hydrated calcium–vanadium silicate, a polymorph of cavansite, known for its electric-blue colour and for acicular crystals in radial or fan-like aggregates.
It forms in cavities of altered basalts under very specific conditions. Growth yields acicular crystals grouped into fans and radial aggregates. The electric-blue colour is intense. Each well-formed specimen is a rarity in this setting.
Significant production has come almost exclusively from India. The Wagholi mines have provided the significant finds. It is much scarcer than cavansite, and perfect crystals are difficult to find.
Etymology
The name refers to the pentagonal arrangement of some crystal groups, observed in ideal views. It was described as a species in 1973.