Andesine-LabradoriteVSColor-Change Garnet

◆Color-change garnet (typically pyrope-spessartine series, (Mg,Mn,Fe)₃Al₂(SiO₄)₃ with V³⁺ ± Cr³⁺ chromophore, Mohs 7.5, SG 3.78–3.84, RI 1.730–1.762, singly refractive isotropic cubic, no pleochroism, moderate-to-strong colour change blue-green-to-red-purple) versus andesine-labradorite (feldspar, Mohs 6–6.5, SG 2.65–2.74, RI 1.543–1.573, biaxial doubly refractive, weak pleochroism, moderate colour change). The specific-gravity difference (3.78–3.84 versus 2.65–2.74) is dramatic and diagnostic. The refractive-index difference (1.730–1.762 versus 1.543–1.573) is unambiguous. The polariscope test is decisive: colour-change garnet shows the dark isotropic cross (singly refractive cubic) while andesine-labradorite shows clear doubling (biaxial doubly refractive). The feldspar twinning lamellae and cleavage directions are diagnostic of plagioclase. The hardness difference (Mohs 7.5 versus 6–6.5) is significant. Color-change garnet from the Bekily-Tranomaro district of Madagascar and East African (Tanzania and Kenya) sources commands $1,000–$5,000+ per carat for fine material — substantially above declared diffusion-treated andesine-labradorite pricing.