Perhaps the most well-known locality for Hauyne is the Eifel Mountains of Germany, especially at the In den Dellen quarries, in Niedermendig. The locality has produced exceptional neon-blue crystals in a pumice matrix
, though they are usually crudely formed.
The classic locality of Monte Somma, Vesuvius, Italy has also produced Hauyne with exceptional blue color, although usually in very small crystals. Large, bluish-white crystals have come from the Alban Hills and Sacrofano, in Rome Province, Latium, Italy. Large Hauyne crystals intergrown with white Gonnardite, and sometimes with a greenish tinge, are found in Sar-e Sang, Kokcha Valley, Badakshan Province, Afghanistan.