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