Dolni Okol, Samokov Municipality, Sofia Province, Bulgaria
Emerald mineralization area near the Urdina Lakes, in the north-western part of the Rhodopes. A Proterozoic metamorphic rock sequence, which consists of micaceous and amphibole-biotite gneisses, amphibolites, and marbles with small lenticular bodies of serpentinized ultramafic rocks, locally altered to amphibole-chlorite and talc-chlorite schists. The metamorphic rocks ae cut by granite pegmatites.Emeralds in the form of well-shaped prismatic crystals, 0.4 to 1.5 cm long have been found only in the phlogopite-oligoclase bodies. The density is 2.694 g/cm³.
Bluish green and light green almost colourless beryls, apatite, margarite, chrysoberyl, allanite, and lesser amounts of fuchsite, rutile, bismutite, fine-scaly muscovite and fine-grained quartz occur with the emerald.
Ref: E.Ya. Kievlenko, Geology of gems, 2003, p. 85