Taaffeite

Refractive Index: 1.7200
Abbe Number: 55.0
Crystal System: Isotropic (cubic)
Formation: Natural
Dispersion Data: Approximate (from n, V)
Fits: 1

Refraction Fits

Fit #1— Cauchy from (n_D, V_D)

Cauchy approximation

Valid 0.38–0.78 µm

$n$

n

= 1.7200

V_{D}

= 55.0

n (λ) = 1.7003 + 0.006853/ λ^{2}

Be-Mg-Al oxide; extremely rare. GIA dispersion 0.019. Source: GIA / Winchell / Liddicoat gemological tables.

Absorption Specimens

Sri Lanka, Sabaragamuwa Province, Ratnapura