Crystal data for sodium chromium `anhydrous alum'

Sodium-chromium `anhydrous alum', NaCr(SO₄)₂ is monoclinic, space group C2/m. Cell dimensions are a = 7.956 (3), b = 5.112 (2), c = 7. 109 (3) Å, β = 92 ° 12′ (6′). Powder diffraction data are given.