Assertion: calcite's crystal | /r/HasProperty | birefringent
Facets:
value: almost always
type: DEGREE
value: often
type: DEGREE
Source sentences:
text: Crystals with non-cubic crystal structures are often birefringent, as are plastics under mechanical stress.
text: Birefringence also plays an important role in second-harmonic generation and other nonlinear optical components, as the crystals used for this purpose are almost always birefringent.