Theralite (from Greek "to pursue") is, in petrology, the name given to calcic foidal gabbro, a plutonic hylocrystalline rock consisting of augite, olivine, calcic plagioclase (labradorite), and nepheline, along with accessories including biotite, magnetite, ilmenite and analcime.
The discovery of theralite was looked forward to with interest as it was of rare occurrence, and as completing the series of basic rocks containing nepheline as an essential constituent.
With the addition of alkali feldspar replacing or becoming more dominant than calcic plagioclase theralites grade into foidal syenite, including shonkinite.
Essexite is a form of silica-undersaturated pyroxene gabbro, containing nepheline and orthoclase as essential constituents, though often in small proportions.
Essexites are usually associated with other alkaline, silica undersaturated to monzonitic intrusive rocks and coeval high-alumina basalts.