Essexite

Essexite ( /ˈɛsəkˌsaɪt/), also called nepheline monzogabbro (/ˈnɛfəˌlɪn ˌmɒnzoʊˈɡæbroʊ, -ˌliːn-/[1][2]), is a dark gray or black holocrystalline plutonic igneous rock.

This favors producing a melt rich in large-ion lithophile elements (LILE) such as potassium, barium, rubidium, cesium, and strontium.

Higher than normal potassium favors the production of orthoclase, which is usually absent from most mafic igneous rocks.

Essexite grades into a nepheline monzogabbro with a decrease in potassium feldspar and an increase in the feldspathoid minerals.

Essexites are generally rich in aluminium, alkalis (sodium and calcium), potassium (>3% K2O), LILE-enriched (strontium, caesium and barium), as compared to tholeiitic basalts and gabbros.