EXAMINATION OF BIOTITE GARNET IJOLITE FROM THE MAGNET COVE ALKALINE INTRUSIVE COMPLEX, ARKANSAS

Ijolite is an unusual igneous rock type that typically forms in silica-undersaturated, continental rift environments. These rocks are usually classified by their abundant amount of modal nepheline (up to 70%) and clinopyroxene, but can often contain significant amounts of garnet, biotite, perovskite, and several other accessory minerals. In the Magnet Cove Alkaline Intrusive Complex, two distinct ijolite ring dikes are located near the core of the complex. Generally, the outer ring is garnet ijolite and the inner ring biotite garnet ijolite, but there is some mixing of these two rock units indicating a complex history of emplacement. Petrographic examination of biotite garnet ijolite indicates major minerals include dark brown schorlomite (Ti-bearing garnet), coarse-grained green phlogopite and euhedral gray nepheline with minor amounts of perovskite, clinopyroxene, apatite and pyrite. Detailed SEM analyses were also performed, including collection of secondary electron and EDS-generated spot analyses and X-ray images.