Meyerhofferite is a hydrated borate mineral, with the chemical formula Ca₂B₆O₆(OH)₁₀·2(H₂O), CaB₃O₃(OH)₅·H₂O or Ca₂(H₃B₃O₇)₂·4(H₂O). It occurs principally as an alteration product of inyoite, another borate mineral.