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).
IMA Status:
Valid Species (Pre-IMA) 1952
Locality:
Ascension Island. Link to MinDat.org Location Data.
Name Origin:
Named for Reginald Aldworth Daly (1871-1957), Professor of Geology, Harvard University, Cambridge, Massachusetts, USA.
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Fleet S G , Zeitschrift fur Kristallographie , 121 (1965) p.349-368, The crystal structure of dalyite
Physical Properties of Dalyite
Cleavage:
{101} Good, {010} Good, {100} Indistinct
Color:
Colorless.
Density:
2.84
Diaphaneity:
Transparent
Fracture:
Brittle - Generally displayed by glasses and most non-metallic minerals.
Hardness:
7.5 - Garnet
Luster:
Vitreous (Glassy)
Streak:
white
Optical Properties of Dalyite
Gladstone-Dale:
CI meas= 0.01 (Superior) - where the CI = (1-KPDmeas/KC) CI calc= 0.007 (Superior) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.208,KPDmeas= 0.2073,KC= 0.2094 Ncalc = 1.59