Assertion: tourmaline's hue | /r/HasProperty | due
Facets:
value: mainly
type: DEGREE
value: to traces of titanium
type: CAUSE
Source sentences:
text: It is thought that the particular hue of black tourmaline is due to traces of titanium embedded in the minerals molecular structure.
text: Green hues are mainly due to traces of chromium and vanadium or iron.