Erzurum has a specific local black stone (Oltu tasi, Jet) which is carved to produce jewelry, rosary beads, key-chains, pipes and boxes.
Oltu stone, which has been carved in Erzurum since the 18th century, is one of the best examples of semi-precious stones to be found in the world. Oltu is excavated generally around Yasakdag, especially in Dutlu, Hankaskisla, Alatarla and Cataksu villages between March and October. There are approximately 600 oltu quarries around this area. Out of a total of 290 quarries in the Central Dutlu Region, 120 quarries are still being worked.
Jet is obtained from mountainous areas which are dug perpendicularly to the general surface and have galleries of 70-80 centimeters (27-31 inches) in diameter where only two or three miners can work. It's a very compact velvet-black mineral of the nature of coal. Beds of this organic substance are 7-8 centimeters (3 inches) in thickness. Jet is formed when fossilized trees are subject to diastrophism resulting in folding.
The most attractive characteristic of oltu stone is that it is very soft when excavated and only begins to harden when it is exposed to the air. Therefore, it is very easy to carve this mineral. It generally comes in black, but can also be blackish brown, grey or greenish. When put near gas, this mineral bursts into flames and leaves behind a certain amount of ash. When rubbed, the oltu stone attracts, by way of static electricity, light substances such as dust.
Various ornaments made from oltu are some of the best examples of Turkish aesthetic arts. Oltu stones are mostly used to make ornaments including rings, earrings, necklaces, bracelets, tie pins, pipes, studs, cigarette-holders, and prayer beads. It is also used in the electric and electronics industries.
Even though artificial jet is produced, it is easy to distinguish the real oltu stone from the artificial. To be certain if a stone is real jet just heat a pin and see if it penetrates the stone, then the mineral is not real jet. Real jet leaves behind brown residue when scraped with a knife. When you take an oltu stone in your hand and blow on it, vapor is left on the stone.