Culnafay is a small remnant of the once extensive diatomite deposits of the Lough Neagh and Lower Bann. Recording the environmental history of the area through part of the Holocene, the deposits are of importance to a number of research specialisms.
The area is of special scientific interest because of its deposits of diatomite and associated materials. Diatomite consists of accumulated diatom frustules with differing amounts of clay, silt, sand and peat. Diatoms are microscopic aquatic plants, surrounded by a silica box, or frustule, of various shapes, depending on the species. The diatomite (also known as Kieselguhr or Bann clay) deposits in Northern Ireland were one of the most extensive freshwater diatomite sequences of post-glacial age in Ireland or Britain.