Fenite

a leucocratic metasomatic rock, a type of alkalic syenite. Fenites usually contain 70–90 percent alkali feldspar and 5–25 percent aegirine; alkali hornblende, sphene, and apatite are accessory minerals. Fenites sometimes contain calcite. Fenites are formed at the contacts of gneisses and granitoids with alkalic or carbonate intrusions. They may retain the banded texture of gneiss; in this case, biotite is completely replaced by alkali hornblende or aegirine. Fenites were described in the Fen area of Norway.