Phonotephrite
Phonotephrite is a strongly alkaline volcanic rock with a composition between phonolite and tephrite. This unusual igneous rock contains 7 to 12% alkali content and 45 to 53% silica content. It can be described as a mafic phonolite or a potassic tephrite. Phonotephrite lava flows and volcanic cones have been identified in Antarctica, Europe, North America and Africa.
