Conchoidal - Fractures developed in brittle materials characterized by smoothly curving surfaces, (e.g. quartz).
Habit:
Tabular - Form dimensions are thin in one direction.
Hardness:
3 - Calcite
Luster:
Adamantine
Streak:
light yellow
Optical Properties of Schumacherite
Gladstone-Dale:
CI meas= -0.038 (Excellent) - where the CI = (1-KPDmeas/KC) CI calc= -0.032 (Excellent) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.1844,KPDmeas= 0.1855,KC= 0.1787 Ncalc = 2.23 - 2.24