Assertion: paraíba tourmaline | /r/HasProperty | coloured by copper
Facets:
Source sentences:
text: Paraíba tourmalines are elbaite tourmalines that are coloured by copper and they possess a reflective index (RI) of 1.603 to 1.648, a specific gravity of 2.82 to 3.10 and their birefringence (the optical property of a material having a refractive index that depends on the polarization and propagation direction of light) is an extremely high 0.013 to 0.024.