Fit #1— Cauchy from (n_D, V_D estimated from REE carbonate)
Cauchy approximation
Valid 0.38–0.78 µm
n
n = 1.7200VD = 30.0
n(λ)=1.6838+0.012563/λ2
REE-Ca fluorocarbonate. Dispersion estimated. n_D from published gemological tables; V_D estimated from REE carbonate because species-specific dispersion is not widely reported. Source: Winchell / GIA / Liddicoat compilations.