Gem-quality corundums with pink, red, orange, yellow, blue, light blue, and green colours, appeared in the world market in 1988. The deposit is 50 km south of Nyassa Lake in the Southern Province of Malawi. Corundum crystals, which range from 0.5 to 3 cm in length, occur in a coarse-grained aggregate of epidote and hornblende within epidotized amphibolites (Henn and Bank, 1990).
Depending on the content of chromium and iron, the refractive index ranges from 1.760 to 1.778, the density varies from 4.04 to 3.96 g/cm³ respectively. Crystals contain solid, gas-liquid and gas-liquid-solid inclusions, hollow channels are also observed.
Ref: E.Ya. Kievlenko, Geology of gems, 2003, p. 60