Weloganite occurs in an alkalic sill which has intruded Ordovician limestone at St-Michel, Montreal Island, Quebec. Chemical analysis of the new mineral is ideally Sr 5 Zr 2 C 9 H 8 O 31 . Weloganite is trigonal, space group P3 (sub 1,2) , hexagonal dimensions a=8.96, c=18.06 A, D m =3.22, D c =3.26 for Z=2. The strongest lines of the X-ray powder pattern are 2.81 A (10), 4.35 (9), 2.59 (7), 2.227 (7), 2.009 (7). The mineral occurs predominantly as yellow crystals which are roughly hexagonal in outline and typically irregular in width.