Evaluation of Turkish black amber: a case study of the Oltu (Erzurum), NE Turkey

Turkish black amber named Oltutaşi in Turkish is one of the best examples of semi-precious stone to be found in the world. It is mainly extracted in the county of Oltu (Erzurum) and surrounding mountains, NE Turkey since the 18th century. At the present time, it is known as ornamental stone and its rosary is very famous worldwide. However, there is no modern review of geological properties of the Oltutaşi and Oltutaşi-bearing deposits. This paper filling this gap presents the results of original research on the subject. The Oltutaşi-bearing deposit with Jurassic-Cretaceous is a flych-character sequence, including limestone, sandstone interbedded with volcanic, sandstone, marl and claystone levels. The Oltutaşi is seen asobserved in the a form of lenses with 0.2 to 75 mm in thick within the Oltutaşi-bearing geological material represented by pebble-sandstone-siltstone alternation, including sandy-claystone and marl levels. These lenses present the folded and faulted structures in parallel with the maincounty rocks due to the tectonic deformation affecting the region. It is seenobserves from microphotographs that Oltutaşi includes dominantly consists of carboncarnone and it includes has fracture filled with resinite and maceral such as fusinite and semifusinite. Also, it is possible to observethere are that euhedral pyrite and hematite minerals generally finely disseminatedin the Oltutaşi organic matter.