Second largest mercury mine in the world
Producing more than 13% of the world’s output, the Idrija Mine was, by its quantity of extracted mercury, the second largest mercury mine in the world. More mercury was extracted only in Almadén in Spain.
More than 3 million cubic metres of ore and gangue were excavated, enough to build Keops' pyramid and half of a second one. The excavated ore was initially raised to the surface in buckets, then in vessels, and finally in carts, crushed into small pieces and then burned, first in piles, later in earthen vessels, and then in various furnaces at temperatures above 600 ºC. At high temperatures, mercury vaporised from the ore, and then thickened again as the temperature cooled. Over a period of five hundred years, 147,000 tons of mercury were obtained by burning/smelting.
Mercury was stored in tightly closed iron containers shaped like bottles, which they called cylinders. As many as 3,132,000 cylinders were filled in Idrija and sold all over the world. The highest price for a cylinder – 880 dollars – was attained in 1968, when mercury consumption was at its peak. In the years that followed, the price of mercury continued to fall due to environmental disasters, and in 1974 reached its lowest price – 74 dollars per cylinder.
Alongside mercury, from the very beginning the Idrija Mine also produced cinnabar (HgS), which it used to make pigments. It supplied world markets with this mineral for more than 300 years. The production of cinnabar in Idrija marked the beginning of development of the chemical industry in Slovenia.