The Formation of Cavansite and Pentagonite in the Wagholi Quarries, Pune, India

Formation conditions of dimorphic minerals cavansite and pentagonite were previously based on theoretical assumptions. In doing so, the associations with other minerals, especially zeolites, that actually occur in nature, were disregarded or incorrectly taken into account. As a result, formation conditions were assumed that are not consistent with those for the associated minerals in the Deccan Volcanic Province. This relates in particular to overestimated high pressure and temperature values, as well as chronological processes of alteration. Long-term field studies and evaluations of numerous samples led to the conclusion that cavansite and pentagonite formed under temperature (approx. 120 °C to 200 °C) and pressure (0.01–0.03 GPa) conditions that are relevant for the associated low-temperature zeolites. Integration of geological and petrographic conditions, as well as crystallization sequences enabled the presentation of a multi-stage mineralization model. It is also explained that, contrary to the original assumption, characteristic pentagonite fivelings are not formed from five, but from six individuals.