A dioctahedral member of the true mica group. The end-member formula is K Al(Fe2+,Mg)□Si4O10(OH)2. Typical range in composition is: viAl/(viAl + viFe3+) = 0.5 – 1.0, Mg/(Mg + viFe2+) ≤ 0.5 (Rieder et al., 1998). Li et al. (1997) described ferro- aluminoceladonite-1M from tuffs in the Murihiku Supergroup, Hokonui Hills, Southland, New Zealand.