A type of igneous rock, specifically a fine-grained basalt or related volcanic rock found in Essex and similar geological formations.
Named after Essex (a county in England) plus the mineral suffix -ite. Geological terms often name rocks after the locations where they were first identified or are abundant.
Essexite is a beautiful example of how geology names minerals and rocks — scientists find something interesting and just name it after where they found it, creating a permanent map in the rocks themselves.
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