Streak White Diaphaneity Transparent to opaque Specific gravity 4.6–4.7 Optical properties Uniaxial (+) Refractive index nω = 1.925–1.961 nε = 1.980–2.015, 1.75 when metamict Birefringence δ = 0.047–0.055 Pleochroism Weak Fusibility Infusible Solubility Insoluble Other characteristics Fluorescent and radioactive, may form pleochroic halos References [1][2][3][4] ↑ Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W. and Nichols, Monte C., ed. "Zircon" (PDF).