Shigaite is a mineral with formula NaAl₃(Mn²⁺)₆(SO₄)₂(OH)₁₈·12H₂O that typically occurs as small, hexagonal crystals or thin coatings. It is named for Shiga Prefecture, Japan, where it was discovered in 1985. The formula was significantly revised in 1996, identifying sodium as a previously unknown constituent.