Formula: K2ZrSi6O15
Phyllosilicate (sheet silicate)
Specific gravity: 2.84
Hardness: 7½
Streak: White
Colour: Colourless, brown
Solubility: Gelatinises with acids (Dana)
Common impurities: Ti,Al,Fe,Mn,Mg,Ca,Ba,P

Plutonic igneous environments

Dalyite is a rare zirconium-bearing phyllosilicate.

At Gjerdingen, Oslo area, Norway, dalyite is associated with pyrophanite, elpidite, monazite, janhaugite and kupletskite (Dana, HOM).

At Serra de Agua de Pau, Azores, Portugal, dalyite occurs in syenite (HOM, Webmin), associated with sanidine, arfvedsonite, quartz, aegirine, fayalite, astrophyllite and pyrrhotite (HOM).

At the type locality, Green Mountain, Ascension Island, Saint Helena, dalyite is a rare accessory in ejected blocks of alkaline granite in trachytic and basaltic tuffs (Webmin, HOM, Mindat). Associated minerals include quartz, aegirine, arfvedsonite and aenigmatite (HOM, Dana).

At Cancarix, Albacete, Spain, dalyite occurs in lamproite (a group of dark-colored volcanic to pyroclastic rocks) (Dana, Webmin, HOM).

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