The sadanagaite group minerals are defined as with 0,5 < A(Na+K+ 2Ca) where Na or K is dominant, and with 1,5 < C(Al+Fe3++2Ti), where Al or Fe3+ are dominant. The W position may contain (OH),F or Cl.
Ferri-sadanagaite is defined with A position: Na dominant C2+ position: Mg dominant C3+ position: Fe dominant W position: (OH) dominant.