Pale tan crystal aggregates of dalyite associated to very minoritary orange brown janhaugite. Both are very rare zirconium minerals. From: Gjerdingen, Nordmarka, Lunner, Oppland, Norway. — Photo: David Hospital · CC BY-SA 4.0
Dalyite
Dalyite is an IMA-recognized mineral species in the silicate class, with the chemical formula K₂ZrSi₆O₁₅.
It crystallizes in the triclinic crystal system (space group P-1).
Key properties: Mohs hardness 7.5; specific gravity 2.84; Vitreous luster; optically biaxial.
IMA symbol Dly, grandfathered status — known before the IMA’s founding, named in 1952.
A rare accessory in ejected blocks of alkalic granite in trachytic and basaltic tuffs (Ascension Island); in syenite (Serra de Agua de Pau, Azores); in lamproite (Cancarix, Spain).
It is found associated with Quartz, aegirine, arfvedsonite, aenigmatite (Ascension Island); sanidine, arfvedsonite, quartz, aegirine, fayalite, astrophyllite.
The name refers to Reginald Aldworth Daly (1871–1957), Professor of Geology, Harvard University, Cambridge, Massachusetts, USA.