Bulgaria is rich in industrial minerals, with 70 types being mined. There are important reserves of rock salt near the town of Provadia (4,4 billion tons). Solnitsata, an ancient town located nearby is believed by Bulgarian archaeologists to be the oldest in Europe and was the site of a salt production facility approximately six millennia ago. The reserves of kaolinite are estimated at 70 million tons, situated mainly in north-eastern Bulgaria – Kaolinovo, Todor Ikonomovo, Senovo and Vetovo. Marble is extracted in the mountainous regions – Pirin, Rhodopes, Strandzha, the western Balkan Mountains. There are important quantities of limestone, gypsum, baryte, perlite, feldspar, granite, etc.