Dear RG members, IUGS is planning a new edition of the classical "Le Maitre" book devoted to the classification and nomenclature of igneous rocks. A group of 17 igneous petrologists (hereafter TGIR - Task Group on Igneous Rocks) is working for three years to update specific definitions or proposing entirely new sections.
As the Chair of the TGIR, I would like to start a discussion with all the interested people that want to give help concerning this task. I and the other members of the TGIR will start posting a series of arguments that will greatly benefit from your comments, so I hope to receive stimulating feedback.
The field “F” in the TAS diagram of Le Bas (2002) is expressly addressed to foidites, albeit the IUGS subcommission writes: “before deciding that the rock should be named a foidite check to see if it is a melilitite”. Considering that more than 90% of the rocks classified melilitites worldwide plot in the F field, we propose to add this name to the F field.
According to Le Bas (2002), if K2O >Na2O and if K2O >2 wt%, the melilitite should be named “potassic melilitite” (if modal olivine is 10%). We believe that the adjective “potassic” for a rock containing down to 2 wt% K2O and
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