Upper Hunza Valley, Hunza District, Gilgit-Baltistan, Pakistan
The deposit is near the settlements of Karimbad and Altiabad in the Great Karakorum Mountains. The Hunza deposits are contained within gneiss-marble metamorphic sequence in NW Karakorum. Ruby- and spinel-bearing marbles occur in layers, 1 to 10 m thick, alternating with garnet-micaceous schists and biotite-plagioclase gneisses.Ruby is accompanied by green, finely crystalline chromian muscovite, local pink, red, violet and blue transparent spinel, as well as accumulations of phlogopite, margarite, chlorite and pargasite.
Most of the extracted corundum crystals are opaque or translucent, and contain abundant cracks and inclusions of finely crystalline carbonate. Transparent crystals are of 1 to 2 carats. The colour of the ruby is brownish-red, pink, purple-red, bright-red, and blood-red. Indices of refraction are 1.762 - 1.770, the density is 3.995 - 3.999 g/cm³.
Pink, violet and almost colourless sapphire is less common than ruby.
Ref: E.Ya. Kievlenko, Geology of gems, 2003, p. 54 - 55