Found in nepheline syenite at the contact between a vein of fine-grained albite and the host rock. A member of the Eudialyte group.
Approved IMA 1998 (Dana # Added)
Poudrette quarry, Mont Saint-Hilaire, Rouville County, Quebec, Canada. Link to MinDat.org Location Data.
Named after John Johnston O�Neill (1886-1966), geologist with the Geological Survey of Canada, Ottawa, and later, Professor of geology, Dean of Science and Dean of Engineering at Mc Gill University, Montreal, Canada.