A particular relation proposed by G.E. Archie between the formation factor (F) and porosity (phi), in which F = 1 / phi^{m}, where the porosity exponent, m, is a constant for a particular formation or type of rock. In the original work, Archie proposed that m lay between 1.8 and 2.0 for consolidated sandstones, and close to 1.3 for loosely consolidated sandstones. m was named the cementation exponent shortly afterwards. This relation is also known as the Archie II equation.