Pegmatite localities, Kukurt river, Gorno-Badakhshan, Tajikistan
The Kukurt, or Turakulominsky, ruby deposit is located in the East Pamir Mountains in the Murgab district of Nagorno-Badakhshan, 25 km south of the settlement of Rangkul.Granite pegmatites with topaz, gem tourmaline and large accumulations of hydrothermal gem-quality scapolite outcrop near the deposit, all of which have contributed to the reputation as the Kukurt gem-bearing area.
The gem-bearing area is in the Kukurt anticlinal fold, which occupies part of the east termination of Muzcol-Rangkul anticlinorium and complicates the southern limb of the large Shatput anticline.
The corundum is disseminated in marbles and is concentrated in thin lenticular bodies, which are conformable with the bedding of the marbles. It occurs with phlogopite, rutile, scapolite, fuchsite and light-coloured kaolin.
Red corundum is widely distributed in the fuchsite zone. The crystals are prismatic, often flattened, up to 3 x 10 cm. One unique crystal was 9 x 17 cm with weight of 1465 g. The largest crystals are developed near the contact with the scapolite zone. Corundum accumulations are most common in the thickest parts of a lense. Rather small corundum crystals (no more than 5 cm long) are found in pure calcite marble in association with fuchsite, graphite and green tourmaline.
Large crystals of corundum are mostly opaque. Small crystals are wholly translucent or transparent. The colour of ruby varies from pink to red of different tints, including bright red ("pigeon's blood"). Large crystals have colour-zoning expressed as blue spots or as central violet-blue core. The main defects are numerous partings and diaspore inclusions.
The material suitable for cutting ranges in size from 1 to 5 mm. The indices of refraction are 1.761 - 1.770, the density is 3.98 g/cm³.
Ref: E.Ya. Kievlenko, Geology of gems, 2003, p. 51 - 53