Abstract: Brianyoungite, which is chemically and structurally related to hydrozincite, occurs as white rosettes (<100 µm) with gypsum on rubbly limestone within the oxidised zone at Brownley Hill Mine, Nenthead, Cumbria. The mineral contains (wt.%) 71.47 ZnO, 9.90 CO₂, 6.62 SO₃ and 10.70 H₂O⁺. Based on 29 oxygen atoms, the empirical formula is Zn_11.73[(CO₃)_3.00,(SO₄)_1.10]_4.10(OH)_15.88 or ideally Zn₃(CO₃,SO₄)(OH)₄. Brianyoungite is either orthorhombic or monoclinic with β very close to 90°. Cell parameters determined by electron diffraction and refined from X-ray powder diffraction data are a = 15.724, b = 6.256 and c = 5.427 Å. Density is > 3.93, < 4.09 g/cm³ (meas.) and 4.11 g/cm³ (calc.); Z = 4. Thermogravimetric analysis, IR and XRD powder data (23 lines) are presented.