Formula: NaCa2Si4O10F Triclinic
Agrellite is a very rare mineral found in mafic, sodium-rich and silicon-poor igneous and metamorphic rocks.
MARATHON COUNTY: Agrellite was found as light-gray prisms as much as 1 cm. in maximum dimension in a leucocratic dike exposed during road construction along I-39 just north of Wausau, Marathon County (Medaris and Fournelle, 2007). This is only the second known occurrence in the world of this mineral.