Brittle - Uneven - Very brittle fracture producing uneven fragments.
Habit:
Platy - Sheet forms (e.g. micas).
Hardness:
4-5 - Fluorite-Apatite
Luster:
Vitreous (Glassy)
Streak:
white
Optical Properties of Herschelite
Gladstone-Dale:
CI meas= 0.036 (Excellent) - where the CI = (1-KPDmeas/KC) CI calc= 0.022 (Excellent) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.2279,KPDmeas= 0.2246,KC= 0.233 Ncalc = 1.48 - 1.5