Hypogene alteration of ussingite from the southern part of the Ilímaussaq intrusion in South Greenland has resulted in the formation of three associations: gmelinite-apophyllite, gmelinite-herschelite-earthy-natrolite, and earthy natrolite alone. Ossingite reacted with late magmatic fluids, producing the secondary minerals either by in situ replacement of the ussingite or in cavities, which may be up to 3 cm across.