Assertion: color tourmaline | /r/HasAspect | birefringence of 0.020
Facets:
Source sentences:
text: Color Green Tourmaline has a specific gravity of 3.06, a refractive index of 1.624 - 1.644, and birefringence of 0.020.
text: Color Pink Tourmaline has a specific gravity of 3.06, a refractive index of 1.624 - 1.644, and birefringence of 0.020.