Generally: XYZ₂O₆

X: larger cation - M₂ site
distorted octahedron: Ca²⁺, Na⁺, Mn²⁺, Fe²⁺, Mg²⁺

Y: M₁
octahedral site: Fe²⁺, Mg²⁺, especially Fe³⁺, Al³⁺, Cr³⁺

Z:
tetrahedral site (4CN): Si⁴⁺, Al³⁺