A new magnesium aluminium phosphate mineral with the ideal formula Mg₅Al₁₂(PO₄)₄(OH)₂₂·nH₂O (n ⋍ 32) has been named aldermanite. It occurs as minute talc-like flakes, partly as an alteration product of fluellite, thinly coating cracks and cavities in a brecciated metamorphosed rock phosphate at Moculta, South Australia. Strongest X-ray diffraction lines are 13.40 Å (100) 002, 7.98 Å (80) 011, 5.55 Å (60) 210; unit cell parameters a= 15.00±0.007, b=8.330±0.006, c= 26.60±0.01 Å, Z = 2.