Abstract: A new sodium aluminium sulphate phosphate has been named peisleyite. It has the ideal formula Na₃Al₁₆(SO₄)₂(PO₄)₁₀(OH)₁₇ · 20H₂O. It occurs as fine-grained, compact, brittle, white material on dumps at Tom's Phosphate Quarry, near Kapunda, South Australia. Strongest X-ray diffraction lines are 12.63 Å (100) 010, 7.82(35) 112¯, 5.41(35) 004, 7.59(30) 111. Unit cell parameters are a 13.31 ± 0.006, b 12.62 ± 0.006, c 23.15 ± 0.01 Å, β 110.0°±0.03°, Z = 2.