From 1929 to 1981 there was a large extraction of fluorite: a mineral widely used in metallurgy as a flux (from the Latin fluere meaning “to melt”); for the production of hydrofluoric acid, a very corrosive acid for glass processing and rustproofing; for the production of fluorine, through the electrolysis of hydrofluoric acid; as an addition to detergents to make clothes shine (especially white clothes) and to tackle the chromatic aberration in camera lenses.
During the 1930s, extraction moved further north to the site known as Lente Martelli, 800 metres long, 70 metres high and 40 metres wide. The extracted material was sent to the washery by cableways, where the useful material was sorted from the embedded rock; much of the mineral was sorted by the taissine, women who crushed the stone by hand, separating the mineral from the rock.
After World War II, mining developed almost exclusively in the Lente Martelli, even though the material was beginning to run out, so much so that, following the emptying of some of the columns containing large pockets of fluorite, numerous internal collapses occurred.
Over the centuries, the sorting of useful ore from waste rock was always done manually or with rudimentary tools; this laborious system of sorting continued to be practised even after industrialisation. So, in 1954, the Laveria del Brembo was installed in the locality of Portiera, a district of Camerata Cornello, a crushing system with a crusher, at a time when the mines had 157 employees.
In 1956, the Società Montanistica Bergamasca was established, which definitively ceased operations on 26th June 1981.