Assertion: mexican opal | /r/CapableOf | read 1.42–1.43 birefringence
Facets:
value: typically
type: DEGREE
Source sentences:
text: Single refractive, often anomalous double refractive due to strain Refractive index Mexican opal may read as low as 1.37, but typically reads 1.42–1.43 Birefringence none Pleochroism