A coarse-grained plutonic rock composed primarily of plagioclase, pyroxene, and feldspathoids like nepheline. It is essentially a nepheline-bearing gabbro or diorite. Because it lacks free quartz and is rich in mafic minerals, it is dense and dark. Petrologists identify essexite to map specific alkaline magmatic events in a region's geological history.
Heard on the job
The core samples from the lower intrusion came back as essexite, which explains the high density readings on the gravimetric survey.
Also heard as
- nepheline monzogabbro